add collections api definition

[philvarner]

Related Issue(s): #134

Proposed Changes:

1. Add Collections conformance class defintion

PR Checklist:

• 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.
• This PR does not make any changes to the core spec in the stac-spec directory (these are included as a subtree and should be updated directly in radiantearth/stac-spec)
• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.

[matthewhanson]

Was this intended to have Link relations for the Landing page here on the Collections endpoint?

[philvarner]

yes. We probably also need to clarify which link relations should exist on the /collections and /collections/{collectionid} endpoints for both this and ogcapi-features.

[matthewhanson]

So no other links required: root, parent?

[philvarner]

I'll improve this example.

[matthewhanson]

This seems fine, but wondering what is it that isn't captured in the existing http://www.opengis.net/spec/ogcapi-features-1/1.0/conf/core conformance class for the /collections endpoint that requires a STAC specific Collections conformance class?

[m-mohr]

This seems fine, but wondering what is it that isn't captured in the existing http://www.opengis.net/spec/ogcapi-features-1/1.0/conf/core conformance class for the /collections endpoint that requires a STAC specific Collections conformance class?

It indicates that the collections are STAC compliant...

[m-mohr]

Interesting PR, would like to review it as it's what we pioneered in the openEO API, but will likely take me some days to go through it.

[philvarner]

@matthewhanson This was Chris's idea, and it's basically to allow a user to advertise STAC-compliant Collections without needing to implement all of OGC API Features, e.g., they only want to implement Collections and Item Search. Ideally, there would be a way to define this without duplicating it from OAFeat, but this is what we have for now.