storage: Send metrics from the origin_add endpoint
Prior to this commit, since the loaders got migrated to use the main endpoint, no metrics were sent for the origins any longer.
This commit fixes it.
It also drops the send_metrics call from the deprecated endpoint origin_add_one (which, as an implementation details calls the other one).
Test Plan
tox
Migrated from D3421 (view on Phabricator)