Various improvements in the installer part:
- Now that apt-secure is required (was not needed for Bullseye), mark the local repository on the image as trusted
- Allows for off-line installation on BIOS and UEFI using either d-i or Calamares
- udeb filtering did not work (the star was used as a literal symbol, not as a wildcard)
- Caching of the Debian installer images when building them from git
- Only when LIVE_BUILD is set, use it and prefer the content found there