Merge branch 'add_commit_stats' into 'master'

Add commit stats

## What does this MR do?
When getting commit by SHA in api it returns commit stats

## Are there points in the code the reviewer needs to double check?
Not sure about test I added do we need separate test or we can just shove stats assertion in test above

## Why was this MR needed?
So api users/clients can get statistics on single commit

## What are the relevant issue numbers?
#20307 

## Screenshots (if relevant)

## 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 !5517

1 files changed, 5 insertions, 0 deletions

diff --git a/doc/api/commits.md b/doc/api/commits.md
index 57c2e1d9b87..2960c2ae428 100644
--- a/doc/api/commits.md
+++ b/doc/api/commits.md
@@ -81,6 +81,11 @@ Example response:
   "parent_ids": [
     "ae1d9fb46aa2b07ee9836d49862ec4e2c46fbbba"
   ],
+  "stats": {
+    "additions": 15,
+    "deletions": 10,
+    "total": 25
+  },
   "status": "running"
 }
 ```