Review issues from community about missing API endpoints

In gitlab-org/gitlab!183590 (comment 2642117787), which was about fixing some inconsistencies on an API docs page, the community contributor mentioned he'd created / was following other issues about similar problems in other pages.

They're mentioned in https://gitlab.kitware.com/utils/rust-gitlab/-/blob/master/src/api/README.md.

I'm not able to fix the underlying issues, unless they're "endpoint exists but is undocumented". I can, at least, make sure the issues are labeled properly and routed to the right teams.

Issue	Disposition
API: deleting merged branches should be a POST,... (gitlab-org/gitlab#523481 - closed)	TBD
API: resetting MR approvals should be a POST en... (gitlab-org/gitlab#523480 - closed)	TBD
API: issue reordering should be a POST endpoint (gitlab-org/gitlab#523479)	TBD
API: dedicated endpoint for issue promotion (gitlab-org/gitlab#523466)	TBD
API: missing group service account PAT query en... (gitlab-org/gitlab#523474)	TBD
API: missing group and project webhook queries ... (gitlab-org/gitlab#523476 - closed)	TBD
API: missing deletion for group approval rules (gitlab-org/gitlab#523478)	TBD
API: dedicated endpoint to delete avatars (gitlab-org/gitlab#523467)	TBD
Creating a commit status endpoint should be mov... (gitlab-org/gitlab#217412)	TBD
Rebase MR endpoint should be POST, not PUT (gitlab-org/gitlab#219324 - closed)	TBD
Access Request Approve endpoint should be POST,... (gitlab-org/gitlab#435861)	TBD