Option to upgrade (dirty flash) existing lineage OS installations to to new major android versions.

[BKLronin]

Currently users have to wipe their data/ installation when upgrading to a new android (lineage) version. The lineage docs describe the possibility to upgrade without data loss and it seems to be considered somewhat safe.

An option in the mentioned adavnced mode to "dirty flash" and keep their data would be appreiciated. This might also be the preferred option for most casual custom users because of f.e. auth apps etc.