repo-updater: Add the ability to manually purge repos
Created by: ryanslade
Add very basic ability to manually purge the oldest deleted or blocked repos from an instance. This is initially only intended for cloud as we have a purge worker that runs on customer instances.
For safety you have to specify a limit and we default to purging 1 repo per second, but this is configurable via a query parameter.
Once we've cleaned up repos on cloud, we can consider enabling the worker on cloud too.
After scheduling some repos to be deleted we can see progress using the
src_repoupdater_purge_success
and src_repoupdater_purge_failed
counters.
Test plan
Tested manually and unit tests added. Will also test with a small number of repos in production.