Have been seeing intermittent failures in the test:
tests/functional/api/test_merge_requests.py::test_merge_request_reset_approvals

Also saw a failure in:
tests/functional/cli/test_cli_v4.py::test_accept_request_merge[subprocess]

Add a call to `wait_for_sidekiq()` to hopefully resolve the issues.

Change it so that:

  GroupMemberAllManager uses GroupMemberAll object
  ProjectMemberAllManager uses ProjectMemberAll object

Create GroupMemberAll and ProjectMemberAll objects that do not support
any Mixin type methods. Previously we were using GroupMember and
ProjectMember which support the `save()` and `delete()` methods but
those methods will not work with objects retrieved using the
`/members/all/` API calls.

`list()` API calls: [1]
  GET /groups/:id/members/all
  GET /projects/:id/members/all

`get()` API calls: [2]
  GET /groups/:id/members/all/:user_id
  GET /projects/:id/members/all/:user_id

Closes: #1825
Closes: #848

[1] https://docs.gitlab.com/ee/api/members.html#list-all-members-of-a-group-or-project-including-inherited-and-invited-members
[2] https://docs.gitlab.com/ee/api/members.html#get-a-member-of-a-group-or-project-including-inherited-and-invited-members

BREAKING CHANGE: As of python-gitlab 3.0.0, the default branch for development
has changed from `master` to `main`.

Rename the 'tools/functional/' directory to 'tests/functional/'

This makes more sense as these are functional tests and not tools.

This was dicussed in:
https://github.com/python-gitlab/python-gitlab/discussions/1468