Allow to set a value for null geometries

[antoniocarlon]

Allow to set a value for null geometries.

The null_geom_value can be set when calling read_carto or when calling Geocoding.geocode. Example:

gc = Geocoding()
gdf, metadata = gc.geocode(df, street='address', city='city', country={'value': 'Spain'}, null_geom_value=BaseGeometry())

Created new tests in test_carto.py but not for test_geocoding.py as they are all skipped.

Related to https://app.clubhouse.io/cartoteam/story/94476/axa-group-error-performing-geopandas-operations-on-carto-dataset-because-of-none-values

[simon-contreras-deel]

👌

[simon-contreras-deel]

Just add a line to the changelog :)