Add support for adding additional dependencies to `setup.py`

[parthea]

See the issue mentioned in https://github.com/googleapis/google-cloud-python/issues/10998#issuecomment-1509873131 where change is needed to the generator to specify additional dependencies that are required when multiple APIs are shipped together. In this case, grpc-google-iam-v1 is required by cloud build v2 but not cloud build v1. Since cloud build v1 is the default version, we need to find a way to add the dependency grpc-google-iam-v1 to setup.py.

See similar issue in gkehub where v1beta1 depends on grpc-google-iam-v1 but v1 does not have that dependency.

https://github.com/googleapis/googleapis-gen/blob/2015275a7dda2ad3d1609f06c4208125c7de8a9d/google/cloud/gkehub/v1beta1/gkehub-v1beta1-py/setup.py#L43

https://github.com/googleapis/googleapis-gen/blob/2015275a7dda2ad3d1609f06c4208125c7de8a9d/google/cloud/gkehub/v1/gkehub-v1-py/setup.py#L38