Persistent Storage: Use LUKS2

Originally created by @je843 on #15450 (Redmine)

Cryptsetup 2.0.x supports the LUKS2 format that includes the Argon2i and Argon2id hash algorithms. Argon2 is a memory-hard hash that strengthens low-entropy passphrases.
Attacker costs should be much higher then the current Cryptsetup 1.X which uses PBKDF2 which hashes with SHA-256.

cryptsetup allows converting existing LUKS volumes to LUKS2. But for the first iteration, let’s only consider using LUKS2 for newly created persistent volumes.

Status and Next Steps

Most of the work was done on (not merged) !256 (closed), aka wip/feature/15450-luks2, already.

Update: what follows is probably not needed anymore thanks to Use zram (!1064 - merged).

Next steps are:

• Bump memory requirements to 3GB (#18040)
• guestfs' luks_open fails with Not enough available memory to open a keyslotNot enough available memory to open a keyslot on some host testing systems