[lib] Introduce threadPermissions.EDIT_THREAD_AVATAR
Summary: Based heavily on changes to D7127. Included EDIT_THREAD_AVATAR everywhere that we were including EDIT_THREAD_NAME (please let me know if that was an incorrect assumption).
Test Plan:
- Start up keyserver and ensure that the migration ran:
- Check roles table to see if expected changes were made:
Reviewers: ashoat, ginsu, kuba
Reviewed By: ashoat, ginsu
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D7313