Remove "PERSISTENCE" Redis functionality and documentation

[axsaucedo]

Currently the PERSISTENCE feature that integrates with Redis is in alpha state as per #2138, however it's currently not tested in the latest versions, and hence it would be best if the references from docs / code are removed in favour of re-thinking what is the best way in which we'd want to achieve persistence, and moreover whether we can just add an example that shows how this would work instead to gather further feedback towards how this can become a feature.