Support for disk encryption via Clevis/Tang was added in #36885.

This works in basic cases where there is only one encrypted disk behind the root partition,
but fails if there are multiple encrypted disk: the passphrase is only replaced with Tang
on the first disk, on the others the passphrase is untouched, leading to password prompts at boot.

There are also some bugs in the support of Clevis/Tang for Ubuntu:
- disk_enc_clevis_tang.erb needs to work with dash (not just bash)
- the check of the minor version in the autoinstall template is broken,
recommendation is also to not rely on the minor version for this OS
- PKG_MANAGER_INSTALL is missing in preseed_autoinstall_cloud_init.erb