[Documentation] GeoNode Upgrade from older versions

[marthamareal]

This needs a clean up and upgrade
https://docs.geonode.org/en/master/admin/index.html#geonode-upgrade-from-older-versions

I would remove the current "Upgrade from ..." and create a new "Upgrade from GeoNode 3". Let's test and document the upgrade procedure from 3.2.2 and 3.3.0, highlighting any technological stack upgrade (Postgresql and Geoserver, etc.).

I would focus on the upgrade of GeoNode proejcts, so the two branches 3.2.x and 3.3.x should be considered to track the changes to settings, env vars (and docker-compose).

I would also add a specific paragraph for the upgrade of Docker based deployments.