initializer/cryptsetup: rework bash entrypoint

[jmxnzo]

Similarly to #1161 , this PR serves as a preliminary step toward moving cryptsetup to a subcommand of the initializer binary. Before translating the Bash entrypoint (used in the initializer binary after merging #1161) into Go code, the script was reworked to allow a cleaner integration of the volume encryption.
There were a few peculiarities in the cryptsetup LUKS standardization that have not been fully addressed in the current version of the entrypoint:

• key is equivalent to passphrase (see the LUKS EXTENSION section in the cryptsetup manual).
• When using the --key-file flag with cryptsetup, the file's contents are unexpectedly treated as a passphrase rather than a cryptographic key.
• Using the keyfile as passphrase won't result in higher entropy of the encryption key. As a result, we can directly use the workload secret and UUID without performing key derivation, because there is no straightforward way to avoid the built-in PBKDF for LUKS in cryptsetup.

e2e/volumestatefulset: https://github.com/edgelesssys/contrast/actions/runs/12764474415/job/35576714135