[lib] refactor joining thread to ops
Summary:
Convert logic for ops approach.
Tested that newUserInfos contains only new/updated users so should not be issues in performance terms.
Depends on D9796
Test Plan:
- Create thread
- Join thread
- Join thread with user not being aware of
Reviewers: tomek
Reviewed By: tomek
Subscribers: ashoat, wyilio
Differential Revision: https://phab.comm.dev/D9797