More granular permission for protected branches
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### Problem to solve
Large repositories and monorepos contain both mission critical code as well as non-mission critical code (documentation, etc). Teams managing these large repositories cannot selectively state which paths/directories have more stringent policies. Today branch protection is all or nothing. This prevents administrators from encouraging contributions to non-mission critical parts of the code.
### Proposal
Provide a mechanism which allows repo administrators detail which paths/directories inside the repository should abide by the branch protection settings and which ones do not.
issue