Make the `disk_label` configuration option optional in the `DiskEncryptionClevis` FSIM

[7flying]

The DiskEncryptionClevis FSIM requires a disk_label configuration option to apply the given clevis bindings. Make this optional and if so, the client should infer which disk label the encryption options should be applied to by looking for the LUKS device.

pub struct ServiceInfoDiskEncryptionClevis {
    pub disk_label: String,
    pub binding: ServiceInfoDiskEncryptionClevisBinding,
    pub reencrypt: bool,
}

Out of scope: handling multiple LUKS devices.

Acceptance criteria:

• The DiskEncryptionClevis FSIM no longer requires an explicit disk_label to work
• If no disk_label is given the client-linuxapp will identify which single device the encryption settings will be applied to
• Tests are done to support both configuration options (aka explicit disk_label vs no disk_label)

[nullr0ute]

What format does the "disk_label" option take? Ultimately we should be able to discover the LUKS partition quite easily, whether by lsblk (probably not) or some API in cryptsetup and associated rust bindings.

[7flying]

What format does the "disk_label" option take? Ultimately we should be able to discover the LUKS partition quite easily, whether by lsblk (probably not) or some API in cryptsetup and associated rust bindings.

It's a string, we usually need '/dev/vdaX' or something like that.

[runcom]

so, it's not really a label, it's more a /dev path - perhaps @puiterwijk remembers more