SaveCodeNowCheck: Add support for list of origins
This will allow distributing the 'load' across multiple origins; so that https://github.com/rdicosmo/parmap does not end up with thousands of visits (which makes swh-storage time out when listing visits)
First step to fix swh/infra/sysadm-environment#4386
Migrated from D8544 (view on Phabricator)