runner: Separate scheduling tasks with and without priority concerns
In effect, this will allow to run 2 runners:
- one for recurring tasks
- one for the save code now
This should decrease the probability of the scheduling tasks for the save code now to be stuck behind the main scheduler runner.
Related to swh/infra/sysadm-environment#3367 (closed)
Test Plan
tox
Migrated from D5826 (view on Phabricator)