method to convert CollectionMetadata to STAC json

[jdries]

Need to improve the as_dict method on CollectionMetadata to generate proper and complete STAC metadata.

[soxofaan]

I'm not sure what you mean here, as CollectionMetadata in the client has no as_dict method.
And the class is basically just a wrapper around STAC(ish) metadata given to the constructor, with accessor methods and properties for common metadata items; it's not really a builder for metadata

[jdries]

my bad, commits got lost, I now fixed it without requiring something in the client
But anyway: for tests but also for user logs, it would be convenient that we can export our metadata into a standardized format.
The most logical one being:
https://github.com/stac-extensions/datacube

[soxofaan]

indeed, we could indeed crank up STAC support/compatibility in a couple of places. Also related:

• Use pystac for STAC handling #133