Reset badgeCount during log out

Summary:
This differential fixes badge count behaviour during log-out. The context is here:
https://linear.app/comm/issue/ENG-5169/badge-count-is-not-reset-when-logging-out.

Test Plan:
Before this diff:

1. Update badge count of app (mark some threads as unread on web)
2. Log out
3. Ensure badge count remains unchanged.

After this diff:

1. Update badge count of app (mark some threads as unread on web)
2. Log out
3. Ensure badge count is cleared.

Reviewers: tomek, atul

Reviewed By: atul

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9824