Assign specific media types to relation types

[m-mohr]

Related Issue(s): None

Proposed Changes:

Clarified which media types should be used for the hierarchical relation types.

Intention is to make clients more aware of checking media types as with OGC API - Records etc. we'll run more and more into examples where the media types could be different.

Example with a child link with JSON & HTML media types: https://api.weather.gc.ca/stac/?f=json
or as a JSON excerpt:

{
   "type":"Catalog",
   ...
   "links":[
      {
         "rel":"child",
         "href":"https://api.weather.gc.ca/stac/msc-datamart?f=json",
         "type":"application/json"
      },
      {
         "rel":"child",
         "href":"https://api.weather.gc.ca/stac/msc-datamart",
         "type":"text/html"
      }
   ]
}

Nothing in the spec disallows this, I think.
And we should not disallow it iMHO, to keep compliant with OGC API - Records.

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.
• I have added my changes to the CHANGELOG
  or a CHANGELOG entry is not required.
• This PR affects the STAC API spec,
  and I have opened issue/PR #XXX to track the change.

[gadomski]

Two questions:

1. Is there a place in the spec where it would be appropriate to link into OGC API - Records to indicate the intent to align? It'd be good to preserve the reason behind this change in the documentation somewhere, and I'm not sure the CHANGELOG is the right place?
2. Is there a place in the spec where it would be appropriate to warn clients/consumers about the need to filter hierarchical links by media type (e.g. how you told me about it in get_child_links/get_item_links: Ensure correct media type stac-utils/pystac#1255)? I'm not sure it would be obvious to new implementors that there could be other item links that they shouldn't load as an Item.

[m-mohr]

Yes, we should probably add what @gadomski proposed.

[m-mohr]

@gadomski Added in 80b75c9

[gadomski]

Needs one header text in a table.

[m-mohr]

@gadomski Fixed, please re-review.