add stac validation to metadata of integrationtests

[jdries]

we have a lot of integrationtests that are batch jobs
it should be simple to add stac validation to all of them, using stac validation library

[soxofaan]

and ideally: also do that kind of validation in the unit tests of openeo-geopyspark-driver , where the develop-test cycle is significantly faster

[jdries]

I already added it to openeo-python-driver to catch basic stuff.

Getting basics working is trivial:

            import pystac
            stac_validator = pystac.validation.stac_validator.JsonSchemaSTACValidator()
            stac_validator.validate(resp.json, pystac.STACObjectType.COLLECTION, stac_version="1.0.0", extensions=[])

still need to figure out support for extensions.