List MR eligible approvers

Created by: sirlatrom

Is your feature request related to a problem? Please describe. glab mr approve currently supports approving an MR. It would be cool if it could also list who can approve based on available MR and/or project level approval rules.

Describe the solution you'd like glab mr approvers could list the eligible approvers.

Describe alternatives you've considered Not implementing it.

Additional context Sometimes there are multiple approval rules, sometimes they can be overridden per MR, sometimes that's not allowed, sometimes there's additionally the CODEOWNERS based approval rules.