Merge branch 'issue-board-api-support' into 'master'

Issue Board API support

## What does this MR do?

Adds support for Issue Board in the API.

## Are there points in the code the reviewer needs to double check?

~~Double check whether the Issue Board list movement fix is needed.~~ 

*Moved to a separate issue.* [#22890](https://gitlab.com/gitlab-org/gitlab-ce/issues/22890)

## Why was this MR needed?

Currently the API offers partial support to a project's Issue Board indirectly through Labels.
This MR adds support for listing, creating, moving and removing board lists.

## Does this MR meet the acceptance criteria?

- [X] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [X] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [X] API support added
- Tests
  - [X] Added for this feature/bug
  - [X] All builds are passing
- [X] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [X] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [X] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [X] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
[#22195](https://gitlab.com/gitlab-org/gitlab-ce/issues/22195)

See merge request !6646

1 files changed, 251 insertions, 0 deletions

diff --git a/doc/api/boards.md b/doc/api/boards.md
new file mode 100644
index 00000000000..28681719f43
--- /dev/null
+++ b/doc/api/boards.md
@@ -0,0 +1,251 @@
+# Boards
+
+Every API call to boards must be authenticated.
+
+If a user is not a member of a project and the project is private, a `GET`
+request on that project will result to a `404` status code.
+
+## Project Board
+
+Lists Issue Boards in the given project.
+
+```
+GET /projects/:id/boards
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `id`   | integer  | yes    | The ID of a project |
+
+```bash
+curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/:id/boards
+```
+
+Example response:
+
+```json
+[
+  {
+    "id" : 1,
+    "lists" : [
+      {
+        "id" : 1,
+        "label" : {
+          "name" : "Testing",
+          "color" : "#F0AD4E",
+          "description" : null
+        },
+        "position" : 1
+      },
+      {
+        "id" : 2,
+        "label" : {
+          "name" : "Ready",
+          "color" : "#FF0000",
+          "description" : null
+        },
+        "position" : 2
+      },
+      {
+        "id" : 3,
+        "label" : {
+          "name" : "Production",
+          "color" : "#FF5F00",
+          "description" : null
+        },
+        "position" : 3
+      }
+    ]
+  }
+]
+```
+
+## List board lists
+
+Get a list of the board's lists.
+Does not include `backlog` and `done` lists
+
+```
+GET /projects/:id/boards/:board_id/lists
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `id`   | integer  | yes    | The ID of a project |
+| `board_id`   | integer  | yes    | The ID of a board |
+
+```bash
+curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/5/boards/1/lists
+```
+
+Example response:
+
+```json
+[
+  {
+    "id" : 1,
+    "label" : {
+      "name" : "Testing",
+      "color" : "#F0AD4E",
+      "description" : null
+    },
+    "position" : 1
+  },
+  {
+    "id" : 2,
+    "label" : {
+      "name" : "Ready",
+      "color" : "#FF0000",
+      "description" : null
+    },
+    "position" : 2
+  },
+  {
+    "id" : 3,
+    "label" : {
+      "name" : "Production",
+      "color" : "#FF5F00",
+      "description" : null
+    },
+    "position" : 3
+  }
+]
+```
+
+## Single board list
+
+Get a single board list.
+
+```
+GET /projects/:id/boards/:board_id/lists/:list_id
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `id`      | integer | yes   | The ID of a project |
+| `board_id`   | integer  | yes    | The ID of a board |
+| `list_id`| integer | yes   | The ID of a board's list |
+
+```bash
+curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/5/boards/1/lists/1
+```
+
+Example response:
+
+```json
+{
+  "id" : 1,
+  "label" : {
+    "name" : "Testing",
+    "color" : "#F0AD4E",
+    "description" : null
+  },
+  "position" : 1
+}
+```
+
+## New board list
+
+Creates a new Issue Board list.
+
+If the operation is successful, a status code of `200` and the newly-created
+list is returned. If an error occurs, an error number and a message explaining
+the reason is returned.
+
+```
+POST /projects/:id/boards/:board_id/lists
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `id`            | integer | yes | The ID of a project |
+| `board_id`   | integer  | yes    | The ID of a board |
+| `label_id`         | integer  | yes | The ID of a label |
+
+```bash
+curl --request POST --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/5/boards/1/lists?label_id=5
+```
+
+Example response:
+
+```json
+{
+  "id" : 1,
+  "label" : {
+    "name" : "Testing",
+    "color" : "#F0AD4E",
+    "description" : null
+  },
+  "position" : 1
+}
+```
+
+## Edit board list
+
+Updates an existing Issue Board list. This call is used to change list position.
+
+If the operation is successful, a code of `200` and the updated board list is
+returned. If an error occurs, an error number and a message explaining the
+reason is returned.
+
+```
+PUT /projects/:id/boards/:board_id/lists/:list_id
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `id`            | integer | yes | The ID of a project |
+| `board_id`   | integer  | yes    | The ID of a board |
+| `list_id`      | integer | yes | The ID of a board's list |
+| `position`         | integer  | yes  | The position of the list |
+
+```bash
+curl --request PUT --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/5/boards/1/lists/1?position=2
+```
+
+Example response:
+
+```json
+{
+  "id" : 1,
+  "label" : {
+    "name" : "Testing",
+    "color" : "#F0AD4E",
+    "description" : null
+  },
+  "position" : 1
+}
+```
+
+## Delete a board list
+
+Only for admins and project owners. Soft deletes the board list in question.
+If the operation is successful, a status code `200` is returned. In case you cannot
+destroy this board list, or it is not present, code `404` is given.
+
+```
+DELETE /projects/:id/boards/:board_id/lists/:list_id
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `id`            | integer | yes | The ID of a project |
+| `board_id`   | integer  | yes    | The ID of a board |
+| `list_id`      | integer | yes | The ID of a board's list |
+
+```bash
+curl --request DELETE --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/5/boards/1/lists/1
+```
+Example response:
+
+```json
+{
+  "id" : 1,
+  "label" : {
+    "name" : "Testing",
+    "color" : "#F0AD4E",
+    "description" : null
+  },
+  "position" : 1
+}
+```