fix(tiles): few fixes around collection-level OGC API Tiles:

[rkettelerij]

• fix landing/conformance page to not include dataset tiles when only using collection-level tiles
• made some fields optional in CRD, since we're inlining a struct in the generated YAML/JSON.

Type of change

• Bugfix

Checklist:

• I've double-checked the code in this PR myself
• I've left the code better than before (boy scout rule)
• The code is readable, comments are added that explain hard or non-obvious parts.
• I've expanded/improved the (unit) tests, when applicable
• I've run (unit) tests that prove my solution works
• There's no sensitive information like credentials in my PR