Changes include:

- Ensure Member.add_user is not called directly when not necessary
- New GroupMember.add_users_to_group to have the same abstraction level as for Project
- Refactor Member.add_user to take a source instead of an array of members
- Fix Rubocop offenses
- Always use Project#add_user instead of project.team.add_user
- Factorize users addition as members in Member.add_users_to_source
- Make access_level a keyword argument in GroupMember.add_users_to_group and ProjectMember.add_users_to_projects
- Destroy any requester before adding them as a member
- Improve the way we handle access requesters in Member.add_user
  Instead of removing the requester and creating a new member,
  we now simply accepts their access request. This way, they will
  receive a "access request granted" email.
- Fix error that was previously silently ignored
- Stop raising when access level is invalid in Member, let Rails validation do their work
Signed-off-by: NRémy Coutable <remy@rymai.me>

Fixes #20456.

This allows web hooks to have a URL back to entities without having to
generate it themselves.

Workflows which use a bot to merge should remove branches if requested.
Expose the flag so that bots can request know this.

Closes #18484

The logic of the method was obviously inverted.
Signed-off-by: NRémy Coutable <remy@rymai.me>

Based on the feedback from reviewers.
Signed-off-by: NRémy Coutable <remy@rymai.me>

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

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

The `sha` parameter is optional, and when present, must match the
current HEAD SHA of the source branch. Otherwise, the API call fails
with a 409 Conflict and a message containing the current HEAD for the
source branch.

Also tidy up some doc wording.

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

Fixes #14692

Added some documentation for it

Added to changelog

Added curl example and an attribute table

Moved the api route definition from "lib/api/issues.rb" to "lib/api/merge_requests.rb"

Fixed the attributes and changed the documentation to be at "merge_requests.md" too

Changed generic titles to more specific titles

added an underscore

added tests. it depends on a newer version of gitlab-test project
I'm doing a  since I need to add a branch to the `gitlab-test` repo

removed the before

using 'iid' instead of 'id' in the description to reference the issues. that makes the tests pass

Removed the 'closes-issues' key from test_env. so it should pass the tests

Moved the two initializations to the describe block

Changed the changelog

* Follow REST for merge request API route
* Remove repeating comments API for MR
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>