Exclude requesters from Project#members, Group#members and User#members

## What does this MR do?

It excludes requesters from the `Project#members`, `Group#members` and `User#members` associations, and adds new `Project#requesters` and `Group#requesters` associations.

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

No.

## Why was this MR needed?

Without this, if you call `project.members`, requesters are included in the results! This is at best misleading, and at worst can lead to security issues. By excluding requesters from the `#members` associations, we avoid introducing security inadvertently since you have to call the `#requesters` association explicitly to get requesters.

## What are the relevant issue numbers?

This is something I realized while fixing the security issue #19102.

## Does this MR meet the acceptance criteria?

- [x] I don't think this needs a CHANGELOG since this is an internal change
- Tests
  - [x] Added for this feature/bug
  - [ ] 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 !4946

And create new Project#requesters, Group#requesters scopes.

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

* upstream/master: (120 commits)
  Update CHANGELOG for 8.9.4, 8.8.7, and 8.7.9.
  Remove additional entries from CHANGELOG
  Catch permission denied errors and ignore the disk
  Remove coveralls lines
  Make GH one-off auth the default again for importing GH projects
  Import from Github using Personal Access Tokens.
  Remove hardcoded gitlab-shell version in test env now that the required tag is published
  Updated breakpoint for sidebar pinning
  Expire branch/tag git data when needed.
  Remove unnecessary parens
  Enable Style/UnneededCapitalW Rubocop cop
  Expiry date on pinned nav cookie
  Fix broken spec in git_push_service_spec by stubbing an external issue tracker
  Handle external issues in IssueReferenceFilter
  Move Changelog entry for build retry fix to 8.9.4
  Add Changelog entry for build sidebar retry link fix
  Improve method that tells if build is retryable
  Do not show build retry link when build is active
  Remove coveralls as its unused
  Move changelot item "Add sub nav to file page view" to 8.9.4
  ...

Loop all disks when displaying system info. Closes #18886



See merge request !4983