datahub: replace karapace URL by datahub GMS API
This will allow us to deprecate karapace and its associated hosts, as they were only there for Datahub.
Bug: T363461
How to register an account on GitLab. Due to spam, new accounts are locked until approved by an admin or the approver bot. Your GitLab account gets automatically approved within one hour if you are a member of Trusted Contributors in Gerrit, or a member of the Trusted-Contributors group in Phabricator and linked your Developer account to your Phabricator account. If none of these apply, you can file an unlock request to expedite access.
Support: mw:GitLab, how to host a project on GitLab, #wikimedia-gitlab on libera.chat, #GitLab on Phabricator.
This will allow us to deprecate karapace and its associated hosts, as they were only there for Datahub.
Bug: T363461