Refactor `metadata_upload` method to upload all the supported metadata fields

[Gpetrak]

In the current version of QGISGeoNode plugin, only title and abstract fields can be updated / uploaded on the remote GeoNode through the plugin:

# src/qgis_geonode/gui/geonode_map_layer_config_widget.py >> upload_metadata()
payload=json.dumps(
    {
        "title": current_metadata.title(),
        "abstract": current_metadata.abstract(),
    }
),

We should refactor the method in order to be abe to upload all the modified fields from the dataset's metadata through the plugin.