Resolve #10 (self link), #11 (completeness), #12 (/collections)

[m-mohr]

Related Issue(s):

• Require self link? #10
• Do entities need to be complete? #11
• Clarify collections from /collections should not be listed #12

Proposed Changes:

1. Each Catalog and Collection listed in the children array must include a self link (#10)
2. Catalogs and Collections in the children array must be complete and valid; reduced entities are not allowed (#11)
3. Clarified that the Collections listed at the /collections endpoint are not implicitly part of the /children response; only entities referenced via child links are included (#12)

I just made a proposal, I'm happy to discuss

• whether to weaken the self-link requirement to a recommendation,
• whether to allow reduced entities
• ...

PR Checklist:

• This PR has no breaking changes.
• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.