Job Results: STAC Collections instead of (or in addition to) Items

[m-mohr]

Due to the fact that Assets have only recently been added to STAC Collections, we currently return STAC Items in job results although it would likely make more sense to expose them as collections with optional items, depending on the data set that has been generated. Fortunately, the assets dict itself is fully compliant to Items.

[m-mohr]

This is something that probably needs to be done via openEO Platform.

[m-mohr]

I'll draft a (somewhat) backward-compatible PR for this as this is getting important.

The idea is to duplicate the assets into Collection Assets, for now, to have the assets available to all clients in a backward-compatible way. I'm checking the client implementations so that they rely on nothing else than assets. Result:

• JS Client: ✔ getResultsAsItem will return something not very meaningful, but somehow handles it gracefully. Other methods work just fine. Will still issue a new version that handles it better.
• Web Editor:😢 Will not correctly render the Collection results, but I'll implement that asap so that it shouldn't block anything.
• R Client: ✔ Uses properties.expires, but it's implemented in a way that it ignores it if not set. Other than that just uses assets.
• Demo App: ✔ Works smothly
• Python client: ✔ Just uses assets, I don't see anything breaking