Automatically fetch Gaia-X credential schemas from Registry/GXDCH

[SchulzeStTSI]

Migrated from GitLab Issue #203

Going beyond #199, rather than just, from time to time, copying over the latest released schemas from the Gaia-X Registry / GXDCH into the XFSC Catalogue Repository and thus the defaults of any new deployed instance, we might enable the XFSC Catalogue to actively fetch "the latest schemas" from the Registry / GXDCH.

[noVaSon]

The reference above actually references another pull request in our organization that was created to collect the changes for our tender FACIS-FCE, before we had committers. So this is not implemented. You have to add a new schema via a framework bundle, if you want to support it.