Add basic LUKS detached header support

Add basic LUKS detached header support

A LUKS root volume with a detached header on a device without partitioning will not have a UUID and will not have an attribute ENV{ID_FS_TYPE}=="crypto_LUKS".
Therefore, several areas need to be addressed: identification of the LUKS device, inclusion of entries within crypttab, and provision of the detached header file.
- Added support for an option (4th column: "force") in /etc/crypttab to force the inclusion of the entry in the initramfs version (avoiding the fs type test).
- Added support for an option (4th column: "header=/path/to/file") in /etc/crypttab to provide a path to a detached header file embedded within the initramfs.
- Added ID and PARTUUID support to the device (2nd column) in /etc/crypttab (complementing the existing UUID functionality).
- Added cmdline support to indicate LUKS device ("rd.luks.serial=") that refers to the attribute ENV{ID_SERIAL_SHORT}.
Tested successfully on Void Linux (x86_64 musl) (no systemd) with a LUKS root volume accessed with a keyfile and using a detached header.
Not tested on systemd, or on a LUKS root volume with a passphrase rather than a keyfile.