Include information on updating mirror synchronization times

+ update_all_mirrors_worker_cron
+ update_all_remote_mirrors_worker_cron

See merge request !763

Document a new gotcha when using `prepend`

See merge request !963

[ci skip]
Signed-off-by: Rémy Coutable <remy@rymai.me>

CE upstream

Unmerged paths: (use "git add/rm ..." as appropriate to mark resolution)

```
both modified:   app/models/namespace.rb
both modified:   app/models/project.rb
both modified:   app/views/layouts/nav/_group_settings.html.haml
both modified:   app/views/projects/_merge_request_settings.html.haml
both modified:   app/views/projects/edit.html.haml
both modified:   app/views/shared/milestones/_summary.html.haml
both modified:   db/schema.rb
both modified:   doc/README.md
both modified:   doc/api/merge_requests.md
both modified:   lib/api/merge_requests.rb
both modified:   lib/gitlab/search_results.rb
both modified:   spec/lib/gitlab/import_export/all_models.yml
both modified:   spec/models/project_spec.rb
both modified:   spec/services/merge_requests/refresh_service_spec.rb
```

See merge request !960

API: Add the project filter to the groups endpoint.

Related to #22928. Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/25420

See merge request !8034

Allow branch names with dots on API endpoint

closes #25030

See merge request !7963

fix: 25294 - remove signed_out notification

Closes #25294

See merge request !7958

Fix alignment for notification settings ajax response

## What does this MR do?

Fixes a issue where an AJAX call to change your global notification settings will return an html partial which has the incorrect dropdown alignment class, in some cases causing the dropdown menu to become obscured on the left side of the screen.

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

## Screenshots (if relevant)

See issue #25510 for a screenshot of the problem and steps to reproduce.

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- Tests
  - [ ] ~~Added for this feature/bug~~
  - [ ] 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 it does - 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?

Closes #25510

See merge request !8024

test: replaced signed_out message check with check for sign_in button

fixes #25294

Adding support for personal snippet endpoint on the API

Closes #22042

See merge request !6373

Fix typo

See merge request !955

Fix typo

See merge request !8029

Fix typo in curl example request

See the general Documentation guidelines http://docs.gitlab.com/ce/development/doc_styleguide.html

## What does this MR do?

Fix a typo in a curl example
Closes #23834 

## Moving docs to a new location?

See the guidelines: http://docs.gitlab.com/ce/development/doc_styleguide.html#changing-document-location

- [ x] Make sure the old link is not removed and has its contents replaced with a link to the new location.
- [ x] Make sure internal links pointing to the document in question are not broken.
- [ x] Search and replace any links referring to old docs in GitLab Rails app, specifically under the `app/views/` directory.
- [ x] If working on CE, submit an MR to EE with the changes as well.

See merge request !8030