Allow STAC API as response for GET /jobs/{job_id}/results

[m-mohr]

For larger results it could be nice to actually expose a (full) STAC API instead of a STAC Collection/Item.

It's a bit diffiult with Catalog (API without assets, but required in openEO for legacy reasons) vs Collections / Items (with assets).

[SerRichard]

If we aim to expose catalogues, it would be nice as a user that I would have access to their own catalogue where job results are linked in as the available collections? This might help for keeping the /jobs/{job_id}/results the same for all current backends. Is a GET for a new endpoint like '/jobs/catalogue' an option?

[m-mohr]

Duplicate of #398