Function cryptsetup_rs::device::luks_add_keyslot

pub fn luks_add_keyslot(
    cd: &mut RawDevice, 
    key: &[u8], 
    maybe_prev_key: Option<&[u8]>, 
    maybe_keyslot: Option<Keyslot>
) -> Result<Keyslot>

Add key slot using provided passphrase. If there is no previous passphrase, use the volume key that is in-memory to add the new key slot.