Migrate catalogue visualisation to catalogue submodule

A while back we crated a CI stage for automatically rendering the most recent version of our DB schema using Schemacrawler.

This stage was sadly not updated when we transitioned to using 'main' as the default branch, and has therefore not been run for a while. We should take the opportunity to move it to the new repo.

TODOs:

• Move the docs CI stage out of this repo's CI and into https://gitlab.cern.ch/cta/cta-catalogue-schema
• Adjust the stage rule to use main instead of master (rule discarded)
• Investigate ways to easily publish the artifact at a public page such as https://eoscta.docs.cern.ch/