Function create_sender_key_distribution_message 

pub async fn create_sender_key_distribution_message<R>(
    sender: &ProtocolAddress,
    distribution_id: Uuid,
    sender_key_store: &mut dyn SenderKeyStore,
    csprng: &mut R,
) -> Result<SenderKeyDistributionMessage, SignalProtocolError>
where
    R: Rng + CryptoRng,