Branch rules MVC: Add GraphQL endpoint to delete the Branch rule

Description

As part of the MVC for organizing rules based on branches, we need to implement new endpoints to support the frontend.

This issue blocks #362217 (closed) and #362218 (closed)

Scope

The scope of this issue includes:

• New endpoint for deleting a branch rule

issue	note
Branch rules MVC: Implement frontend skeleton (#362205 - closed)
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)	👈 this issue ⚠ 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