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

Submit new issues created via the WebUI or API to Akismet for spam check on public projects.

## What does this MR do?

Submit new issues created via the WebUI by non project members to Akismet for spam check.

## Why was this MR needed?

Support for Akismet was added only to the API with !2266. This MR builds on that functionality to also check issues submitted via the WebUI for spam.

## What are the relevant issue numbers?

Related to:

- #5573 
- #5932 
- gitlab-com/infrastructure#14
- gitlab-com/support#61
- !2266

cc @stanhu @MrChrisW 

See merge request !5333

This was missing from gitlab-org/gitlab-ce!5509.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Add missing escape at line end

Documentation fix, pretty simple.

See merge request !5422