/processes endpoint improvements

[clausmichele]

Currently the /processes endpoint exposes the content of two json files containing the set of processes implemented in Python and WCPS. We should expose only the ones for Python if no WCPS Collection is exposed. See here:

openeo-spring-driver/src/main/java/org/openeo/spring/api/ProcessesApiController.java

Line 131 in 657d268

final Map<Resource, EngineTypes> res2eng = new LinkedHashMap<>();

Additionally, instead of a file based, we can use the /processes endpoint I added to the openeo_odc_driver here: https://github.com/Open-EO/openeo_odc_driver/blob/6a6b3a9dd43496477a0e915e0911f9757782582b/openeo_odc_driver/odc_backend.py#L177