Create stub GraphQL API SetRepositoryPermissionsForBitbucketProject

Created by: indradhanush

Part 1 for #36454 (closed).

At the moment, the API doesn't really do anything apart from running some validation checks. Once we have the Bitbucket permissions worker implemented, this API will trigger a sync job and return a job ID or equivalent in the response instead of the currently empty response that it returns at the moment.

Test plan

Added new unit tests for the implemented functionality.