api.checks: Warn when suggested fields are missing from metadata
This introduces a new check about the metadata provenance. While it's a suggested field, it's definitely something that we want deposit clients to send us. So warn when it's not the case. That does not reject the deposit but it's worth keeping that detail in the backend.
Related to #3677 (closed) Depends on !278 (closed)
Test Plan
tox
Migrated from D7209 (view on Phabricator)