graphqlbackend: add endpoint to list Bitbucket Projects permission sync jobs

Created by: sashaostrikov

Adding of a GraphQL endpoint which lists Bitbucket Projects permission sync jobs.

A small description of changes, which I hope helps in review:

• authz.go contains gql resolver interfaces and endpoint input args struct
• bitbucket_projects_permission_jobs.go contains gql resolvers implementation
• resolver.go contains endpoint logic (input validation + db queries)

Closes https://github.com/sourcegraph/sourcegraph/issues/36455

Test plan

Added a unit test, tested manually on local sg instance with different input combinations.