Remove `keep_divergent_refs` feature flag, adding documentation and changelog
Feature added in:
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/25639
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/26405
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/26406
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/26407
Feature expanded in:
- https://gitlab.com/gitlab-org/gitaly/-/merge_requests/1915
- https://gitlab.com/gitlab-org/gitaly/-/merge_requests/2028
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/29082
## Internal rollout and testing
1. [x] See ae62fb08ccdb1a2dba0706e98a0db19bc9f2dd99 through to production.
1. [x] Enable `keep_divergent_refs` feature flag for projects that have a Canonical -> Security -> Build mirroring structure. Note the flag is scoped to projects, not groups.
1. [x] Enable `keep_divergent_refs` for all of our push mirrors via API:
```sh
$ http GET 'https://gitlab.com/api/v4/projects/gitlab-org%2Fgitlab/remote_mirrors/'
[
{
"enabled": true,
"id": 177728,
"keep_divergent_refs": false,
"last_error": null,
"last_successful_update_at": "2020-04-28T19:35:34.695Z",
"last_update_at": "2020-04-28T19:35:34.695Z",
"last_update_started_at": "2020-04-28T19:36:42.044Z",
"only_protected_branches": true,
"update_status": "started",
"url": "https://*****:*****@gitlab.com/gitlab-org/security/gitlab.git"
}
]
$ http PUT 'https://gitlab.com/api/v4/projects/gitlab-org%2Fgitlab/remote_mirrors/177728' keep_divergent_refs=true
```
## General release
- [x] Remove feature flag check
- [x] Add changelog entry
- [x] Add API documentation
- [x] Add User documentation
- [x] Internationalization
- [x] Address spec nitpick from https://gitlab.com/gitlab-org/gitlab/-/merge_requests/29082#note_333135591
- [x] Delete feature flag entry via ChatOps
issue