dracut does not support booting from an encrypted ZFS volume

[Benjamin Drung]

Dracut does not support booting from an encrypted ZFS volume. Steps to reproduce:

1. In a VM install Ubuntu 24.10 with an encrypted ZFS volume
2. Install dracut afterwards: sudo apt install dracut zfs-dracut
3. Add rd.shell to the boot arguments
4. Reboot

The boot will fail:

```
dracut-pre-mount[817]: Warning: ZFS: Key /run/keystore/rpool/system.key for rpool hasn't appeared. Trying anyway.
dracut-pre-mount[863]: Key load error: Failed to open key material file: No such file or directory
[FAILED] Failed to mount sysroot.mount - /sysroot.
```

The initrd should have asked for the password, but it did not.

ProblemType: Bug
DistroRelease: Ubuntu 24.10
Package: dracut-core 102-3ubuntu2
ProcVersionSignature: Ubuntu 6.8.0-31.31-generic 6.8.1
Uname: Linux 6.8.0-31-generic x86_64
NonfreeKernelModules: zfs
ApportVersion: 2.28.1-0ubuntu4
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Fri Jun 21 09:35:42 2024
InstallationDate: Installed on 2024-06-20 (1 days ago)
InstallationMedia: Ubuntu 24.10 "Oracular Oriole" - Daily amd64 (20240617)
ProcEnviron:
 LANG=de_DE.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 TERM=xterm-256color
 XDG_RUNTIME_DIR=<set>
SourcePackage: dracut
UpgradeStatus: No upgrade log present (probably fresh install)