Merge branch 'issue_8110' into 'master'

Allow slack service to send messages on different channels

closes #8110 

## Allow slack service to send messages on different channels  

![new_slack_service](/uploads/87de0bd6b02a4f7853358676b5e74dff/new_slack_service.png)

## 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 [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)

See merge request !5124

4 files changed, 29 insertions, 4 deletions

diff --git a/doc/integration/slack.md b/doc/integration/slack.md
index f6ba80f46d5..11f956fed3e 100644
--- a/doc/integration/slack.md
+++ b/doc/integration/slack.md
@@ -26,14 +26,13 @@ After Slack is ready we need to setup GitLab. Here are the steps to achieve this
 
 1.  Navigate to Settings -> Services -> Slack
 
-1. Pick the triggers you want to activate
+1. Pick the triggers you want to activate and respective channel (`#general` by default).
 
 1.  Fill in your Slack details
     - Webhook: Paste the Webhook URL from the step above
     - Username: Fill this in if you want to change the username of the bot
-    - Channel: Fill this in if you want to change the channel where the messages will be posted
     - Mark it as active
-    
+
 1. Save your settings
 
 Have fun :)
diff --git a/doc/project_services/img/slack_configuration.png b/doc/project_services/img/slack_configuration.png
new file mode 100644
index 00000000000..d3ebe5969af
--- /dev/null
+++ b/doc/project_services/img/slack_configuration.png
diff --git a/doc/project_services/project_services.md b/doc/project_services/project_services.md
index e15d5db3253..4442b7c1742 100644
--- a/doc/project_services/project_services.md
+++ b/doc/project_services/project_services.md
@@ -45,7 +45,7 @@ further configuration instructions and details. Contributions are welcome.
 | PivotalTracker | Project Management Software (Source Commits Endpoint) |
 | Pushover | Pushover makes it easy to get real-time notifications on your Android device, iPhone, iPad, and Desktop |
 | [Redmine](redmine.md) | Redmine issue tracker |
-| Slack | A team communication tool for the 21st century |
+| [Slack](slack.md) | A team communication tool for the 21st century |
 
 ## Services Templates
 
diff --git a/doc/project_services/slack.md b/doc/project_services/slack.md
new file mode 100644
index 00000000000..4ed33838f7c
--- /dev/null
+++ b/doc/project_services/slack.md
@@ -0,0 +1,26 @@
+# Slack Service
+
+Go to your project's **Settings > Services > Slack** and you will see a checkbox with the following events that can be triggered:
+
+* Push
+* Issue
+* Merge request
+* Note
+* Tag push
+* Build
+* Wiki page
+
+Below each of these event checkboxes you will have an input to insert which Slack channel do you want to send that event message,
+`#general` channel is default.
+
+
+![Slack configuration](img/slack_configuration.png)
+
+
+| Field | Description |
+| ----- | ----------- |
+| `Webhook`   | The incoming webhook url which you have to setup on slack. (https://my.slack.com/services/new/incoming-webhook/) |
+| `Username`   | Optional username which can be on messages sent to slack. |
+| `notify only broken builds`    | Notify only about broken builds, when build events are marked to be sent.|
+
+