Support `VectorCube` type as `spatial_extent` in `load_collection`

I get an error when providing vector data as spatial_extent in load_collection:

{'loadurl1': {'process_id': 'load_url',
  'arguments': {'format': 'Parquet',
   'url': 'https://artifactory.vgt.vito.be/artifactory/auxdata-public/gfmap/32736-random-points.geoparquet'}},
 'loadcollection1': {'process_id': 'load_collection',
  'arguments': {'bands': ['NDVI_10M'],
   'id': 'TERRASCOPE_S2_NDVI_V2',
   'spatial_extent': {'from_node': 'loadurl1'},
   'temporal_extent': ['2022-05-01', '2022-05-30']},
  'result': True}}

This process graph results in OpenEoApiError: [500] Internal: Server error: AttributeError("'DriverVectorCube' object has no attribute 'get'")

It's not a blocking issue for me, as there is an easy workaround, by just omitting the spatial_extent in load_collection. However, could we already provide a clearer error message in the meantime?

CC: @Pratichhya

Start by reproducing the shown process graph in load_collection with the VectorCube spatial_extent and trace where the DriverVectorCube object is treated like a mapping. Determine whether the intended outcome is VectorCube support or a clearer validation error, then verify the selected behavior against the reported workaround of omitting spatial_extent.