[suggestion] Expose luks cypher as parameter/tunable

[eleius]

It would be nice if the algorithm used for LUKS in src/installation/auto_partition.py (currently defined by the "cypher" variable) could be changed via a simple command line parameter (something like: cnchi --luksalgo:aes-xts-plain64) and maybe also --key-size and --hash

[eleius]

I saw a luks_options.get for cypher, password and key in the new cnchi, thanks for implementing the change! How do I set these so as to make cnchi use a different key size or algorithm?