v4.2.1

Release components in a single tag GeoNode 4.2.1 depends on. Includes the images:

• https://hub.docker.com/r/52north/geonode-geoserver
• https://hub.docker.com/r/52north/geonode-geoserver_data
• https://hub.docker.com/r/52north/geonode-nginx
• https://hub.docker.com/r/52north/geonode-postgis