API: assigned_to_me scope equivalent for reviewers

Hello team,

Proposal

In the API for the merge requests the scopes are assigned_to_me | created_by_me | all (see doc).

That said it does not include the new feature of reviewers. I suggest the addition of a new scope like reviews_for_me (i think there is better wording that this) that will send back all the the MR where the current user is set as a reviewer. Or it could be that the scope assigned_to_me sends back both MR where you are reviewer and assignee.

For now when you want this you need to make three calls, one to get the current user id, one to get assigned MRs and one to get reviewer MRs.