[server] Create script to add LEAVE_THREAD permission

Test Plan:
Tested on a single row to check if results are matching expectacions.
Inspected membership table to check if leave_thread permission is added. Inspected roles table to check if permission is added.
Ran a query after the script, and made sure only personal threads are in the result:
SELECT * FROM roles WHERE JSON_EXTRACT(permissions, "$.leave_thread") IS NULL
Checked if leave thread button is displayed and after pressing there are no errors and user leaves thread

Reviewers: ashoat, palys-swm

Reviewed By: ashoat

Subscribers: zrebcu411, Adrian

Differential Revision: https://phabricator.ashoat.com/D466