collab: Add `username` to `User` (#60097)

This PR adds the `username` field to `User` and `proto::User`.

Closes CLO-949.

Release Notes:

- N/A
0a7c84bc37Marshall Bowers committed on 6/29/2026, 3:06:18 PM· committed by GitHubparent485aeab
8 files changedLine totals unavailable