Deprecate (or drop) GeometryCollection support

[soxofaan]

triggered from #682: we allow GeometryCollection as GeoJSON type, but that's actually an anti-pattern (e.g. see Open-EO/openeo-processes#389)

openeo-python-client/openeo/rest/datacube.py

Lines 630 to 632 in d5180c3

	valid_geojson_types = [
	"Point", "MultiPoint", "LineString", "MultiLineString",
	"Polygon", "MultiPolygon", "GeometryCollection", "FeatureCollection"

openeo-python-client/openeo/rest/datacube.py

Lines 1197 to 1199 in d5180c3

	valid_geojson_types = [
	"Point", "MultiPoint", "LineString", "MultiLineString",
	"Polygon", "MultiPolygon", "GeometryCollection", "Feature", "FeatureCollection"

openeo-python-client/openeo/rest/datacube.py

Lines 1474 to 1477 in d5180c3

	valid_geojson_types = [
	"Polygon",
	"MultiPolygon",
	"GeometryCollection",

openeo-python-client/openeo/rest/datacube.py

Line 2058 in d5180c3

valid_geojson_types = ["Polygon", "MultiPolygon", "GeometryCollection", "Feature", "FeatureCollection"]

We should get rid of that. I'm not sure if we should first deprecate it with warnings, or just drop support without deprecation phase