Add approval rules drawer to branch rules page

What does this MR do and why?

1. Replaces the current Approval rules section with the shared approval rules app
2. Ensures Editing/Adding approval rules use the approval rules drawer

MR acceptance checklist

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Screenshots or screen recordings

Before	After	After (add)

How to set up and validate locally

1. Enable the approval_rules_drawer feature flag
2. Add a Branch rule
   • Navigate to Project > Repository > Settings > Branch rules > Add branch rule
3. View the branch rule created in step 1
   • Navigate to Project > Repository > Settings > Branch rules > View details
4. On the Branch rule details screen the Approval rules app should display and work as expected
5. Edit/Add should should a drawer containing the approval rule form

Related to #439397 (closed)