Removed meteo extractor

[GriffinBabe]

@HansVRP I removed the METEO fetcher as the same functionalities are present in the METEO fetcher

[VincentVerelst]

One question: this does mean we don't support fetching meteo from the openeo STAC API anymore. Should we then maybe add an assertion that if "AGERA5" is selected, only the terrascope backend can be used?

[GriffinBabe]

@VincentVerelst I added the functionality build_generic_extractor_stac to continue supporting stac extraction, and added some checks based on the backend.

From a discussion with @HansVRP we decided that GFMAP shouldn't take too much care of checking if a collection is valid or not in a certain backend but rather instead let the load_collection method raise the exception itself.

[GriffinBabe]

@VincentVerelst can you review this PR ?