Create rake task to handle OAuth setup from Omnibus managed services
In omnibus-gitlab!3272 (merged) Omnibus is setting up an OAuth application for Grafana automatically.
It relies on injecting ruby code to the rails terminal via /opt/gitlab/bin/gitlab-rails runner
. This is not ideal as any change on GitLab can break the integration without anyone noticing. Testing this is also not easy, as we are not defining an interface between the two applications, but relying on knowledge of the internal implementation.
We should build instead a rake task that would provide the functionality Omnibus require and use that instead. It should cover Pages and Mattermost needs as well (looks like they all operate in a similar way).
This can also be used for other types of distribution like the Helm charts.