Support STAC API in GFMapJobManager & separate STAC management in different class

[VincentVerelst]

Currently, the GFMapJobManager writes static STAC collections to disk. For very large job databases this quickly becomes unfeasible. Therefore, we need to support STAC API's to write asset STAC metadata.

WorldCereal/worldcereal-classification#144

[GriffinBabe]

@VincentVerelst have you in mind a STAC API implementation to recommend for this task? A repository link or some examples would be helpful

[GriffinBabe]

This issue should also contain a fix for #137

Basically create a separate class to manage STAC collections in the GFMAP manager. One way of doing it would be to create a base abstract class for the GFMAPJobManager to interract with stac elements and derived classes for different implementations (for example: local pystac catalogue, or interraction to a STAC server with pystac_client)

[VincentVerelst]

I suggest to split this in two PR's:

• One for the separate STAC management
• One for the STAC API support