wfa.measurement.access.v1alpha.Roles/DeleteRole should throw FAILED_PRECONDITION when PolicyBindings exist

[SanjayVas]

This currently throws an error with status code INTERNAL. The error from the internal service is

io.grpc.StatusException: FAILED_PRECONDITION: Foreign key constraint violation when deleting or updating referenced row(s): referencing row(s) found in table `PolicyBindings`.

There may be some work needed to update the internal service so the public service can accurately identify the error and throw one with more actionable information.