Do not generate images locally but instead generate signatures locally
and use images from offical mirror.

- generate ipxe boot script from template
- add option to start sshd with firstboot
- add version information when selecting branch
- verify netboot releases with gpg signature
- added ncopa.asc gpg public key

- support x86(_64) and arm64
- support for packet.net
- add shell and reboot to menu
- allow setting of console
- allow adding custom cmdline options