WIP: Adds configuration to admin dashboard to restrict push mirorring to a group.

What does this MR do?

Adds the configuration option in the admin dashboard to restrict the push mirroring feature to a specific group.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #1144 (closed)