Reviewer drawer: Presentation of required approver count
## Proposal
Align presentation of approval count to how it is currently presented in MR list.
Doesn't make a lot of sense to have two ways of communicating the same information.
## Concept
From https://gitlab.com/gitlab-org/gitlab/-/merge_requests/168428#note_2158420909
Adding a progress bar to help the "Assign" button can anchor to.

That presentation of "1 of 2" would align to how we present approvals in the MR list https://gitlab.com/gitlab-org/gitlab/-/merge_requests/148364. This presentation would still work for the proposed changes in https://gitlab.com/gitlab-org/gitlab/-/issues/499064+ when all required approvals have been given.
**Blocker**: Required to be solved is how to present the scenario of optional approvals.
issue