Update to latest STAC version

[m-mohr]

Update the data discovery to follow STAC v0.6.x or 0.7 + relevant extensions such as EO and SAR (and also include a preliminary version of the Datacube extension).

[m-mohr]

I updated to STAC 0.6.2-dev and added the SAR + datacube fields (both are still in development so may still change).

[m-mohr]

There's still the new and required cube:dimension parameter missing in the example for /collections/:collection_id and cube:dimension may have changed before the API release, so note to myself: check back before the release. Also, there's an issue with ReDoc: Redocly/redoc#810

[m-mohr]

The cube:dimensions have changed in the STAC draft, we need to update them in the API.

[m-mohr]

Updated the API specification. Last step is to check the links to the v0.6.2 tree after radiantearth/stac-spec#412 has been merged and released.