Add documentation for passwords from secrets
Use password secret for Arch Linux example
Use password secret for Alpine example

And update Alpine version.
Use password secret for Debian example
Support setting user passwords from secrets

Even if it's just the hashed & salted passwords that are currently
exposed, it still presents a certain attack vector. This commit allows
passwords to be moved into secrets, avoiding this vector.

Documentation tbd.
Build packages on and for Alpine 3.18
Revert "Mount host's efivars if present"

This reverts commit 8f524d6b38f83ab2bef467b8123c5c4dbaef0d1f.

It's not needed and mostly provides a giant foot gun...
Mount host's efivars if present

This allows for the preparation of EFI bootable images on hosts that
support EFI.
Add links to packages
Support custom postprocess funtion
Add generated APKBUILD to gitignore
Fix conversion script for nested directories
Fix copy-pasta in rsync destination
build.yml: set packager key
build.yml: add missing packages