Make role argument of `.add` keyword only.
Make role argument of `.add` keyword only.

PiperOrigin-RevId: 433762448
Change-Id: I98aff37f00d56d5f431d4973713c51f1526e30a8
GitOrigin-RevId: 25db2846b5685cd800c61cf878867419e54c87ce

deepmind/xmanager,deepmind/xmanager