Branch rules MVC: Implement frontend skeleton

Description

As part of the MVC for organizing rules based on branches, we need to implement the skeleton/foundation on the frontend that we'll use to build the rest of the feature.

Scope

The scope of this issue includes:

• Add Branch rules section in repository settings behind a feature flag (empty)
• Set up a new Branch rules page (empty)
• Add Branch rules endpoint to Project routes (ensures we can visit the new branch rules page)

Implementation plan

issue	note
Branch rules MVC: Implement frontend skeleton (#362205 - closed)	👈 this issue
Implement the ability to add branch Protections (#362212 - closed)
Implement the ability to add Merge Request appr... (#362214 - closed)
Branch rules MVC: Design or reuse the database ... (#362705 - closed)
Branch rules MVC: Add GraphQL endpoint to suppo... (#362706 - closed)	⚠ blocked by #362705 (closed)
Branch rules MVC: Add GraphQL endpoint to updat... (#362707 - closed)	⚠ blocked by #362705 (closed)
Branch rules MVC: Add GraphQL endpoint to delet... (#362219 - closed)	⚠ blocked by #362705 (closed)
Branch rules MVC: List branch rules under Repos... (#362217 - closed)	⚠ blocked by #362219 (closed)
Implement the ability to Delete a Branch rule (#362218 - closed)	⚠ blocked by #362219 (closed)

Mockups

Mockups can be found in the MVC issue