refactor: Switch ARGs, provide defaults, add aliases. Basically, merge the three dockerfiles into one.

ci: Manually build multiarch image as we are dealing with a BASEimage here. Want to do things from ground up as possible.

secure custom folders

Use jq to parse JSON

Also catch 1969, move banner.

Update s6-overlay to v2.2.0.3 for focal

Add warning regarding time being out of sync on armv7l

Requires linuxserver/docker-documentation#32 to be merged