Updates for openeo API v1.2 and openeo-processes v2.0.0

[soxofaan]

Upcoming API/spec updates:

• Release v1.2.0 openeo-api#492
• Release v2.0.0-rc.1 openeo-processes#439

This is central/epic ticket to follow up necessary coverage of these changes in the python client

[soxofaan]

sub-issues and references:

• Add load_stac #425

[soxofaan]

related to Open-EO/openeo-python-driver#195 in openeo-python-driver

[soxofaan]

• load_geojson
• load_url

also see Open-EO/openeo-python-driver#211

spin off ticket: #457