Validate common metadata also in Catalogs, Collections and Links. Also, re-uses the schemas from common metadata in Collections so that they don't diverge (which was the case).
Includes a very minor somewhat breaking change: Provider, Asset and Item descriptions can't be empty now. Either they need to be omitted or contain at least one character. This aligns with Catalog and Collection description as part of the common metadata model.
PR Checklist:
[x] This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
[ ] This PR has no breaking changes.
[x] I have added my changes to the CHANGELOGor a CHANGELOG entry is not required.
[ ] This PR affects the STAC API spec,
and I have opened issue/PR #XXX to track the change.
Related Issue(s): #1199 #1187
Proposed Changes:
PR Checklist: