Route priority tasks to dedicated save code now queues
This splits the calls to read tasks into 2 calls, one for tasks with no
priority (standard), another call for tasks with priority. If any tasks with priority
are detected, they are routed to dedicated save_code_now:
prefixed named queues (per
task type).
Related to swh/infra/sysadm-environment#3084 (closed)
Test Plan
tox and docker (D5526) and partial successful deployment of this on staging
Migrated from D5520 (view on Phabricator)