do not auto-add save_result when export_workspace is used

[jdries]

Current behaviour: https://github.com/Open-EO/openeo-python-client/blob/29ae888f83a9cecea1e2b260167f02f38417d86b/openeo/rest/datacube.py#L2079

If last node is not save_result, then add it automatically.

Better: check the entire graph for save_result processes? If there are any, then the user probably knows what he's doing.

[soxofaan]

Indeed, there is quite some technical debt to clean up around "save_result" handling. Related tickets:

• https://github.com/Open-EO/openeo-python-client/issues/583
• https://github.com/Open-EO/openeo-python-client/issues/402
• https://github.com/Open-EO/openeo-python-client/issues/401
• https://github.com/Open-EO/openeo-python-client/issues/391

[soxofaan]

started working on draft at #630

[soxofaan]

done with 58f0205db63efbc860b99477cc5e5dea6069224b