Edit Branch Rules: Branch Protection: Implement Allowed to push and merge section with edit

Context

See #362212 (closed)

Mockups

Figma

Allowed to push and merge

• Allows editing of roles, users, groups, and deploy keys
• Default: (empty)
• Empty state text: Everyone is required to submit a merge request for changes.
• On change, display toast "Allowed to push and merge updated"
  • Undo action would be nice to have.

Default	Edit - filled	Allowed to push and merge updated