mention new spatial_extent in docs

Author: jdries

docs/udp.rst

@@ -133,6 +133,8 @@ Some useful parameter helpers (class methods of the :py:class:`~openeo.api.proce
     a parameter for specifying a temporal interval with "start" and "end" dates.
 -   :py:meth:`Parameter.geojson() <openeo.api.process.Parameter.geojson>` to create
     a parameter for specifying a GeoJSON geometry.
+-   :py:meth:`Parameter.spatial_extent() <openeo.api.process.Parameter.spatial_extent>` to create
+    a spatial_extent parameter that is exactly the same as the corresponding parameter in `load_collection` and `load_stac`.