Support load_result -> load_stac rename (openeo-processes 2.0)

[soxofaan]

with Open-EO/openeo-processes#413 (not merged yet at the moment) load_result will be renamed to load_stac (and support for a single batch_job id (string) will be dropped) in v2.0.0 of openeo-processes.

we need to properly support this back-end side (at least python driver I guess)

[soxofaan]

(python client twin ticket: Open-EO/openeo-python-client#398 )