Set approvals list based on AD group

Description

When setting approvals for projects, you're able to set the approvals based on individual users or GitLab Groups

Proposal

In some cases, we've had some of our users request to set their approvers based on AD groups. This way, even if a group has say 3 AD groups tied to master, you can just specify one of those AD groups in the list to say who can approve the code (in case the project doesn't necessarily fall under ALL the masters, but other projects do).

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Hope that makes sense. :)