ZFS related binaries like `zpool`, `zfs` and `zdb` were missing from the kexec image.
This PR fixes the following issues I encountered during testing in the OVH "Public Cloud":
- Machines pre-installed with Debian 11 print error `zdb: command not found` during `disk-deactivate` when trying to remove `/dev/sda14`
- Trying to create a simple zpool + zfs dataset that is mounted as `/` fails with `zpool: command not found`
On OVH machines the installer would print an error being unable to locate the `zdb` binary,
