Display content of `InvalidType` in `fe2o3-amqp-management`'s `Error::DecodeError`

[minghuaw]

The current error message if printed is not helpful

/// Error type for the management client.
#[derive(Debug, thiserror::Error)]
pub enum Error {
    // ...

    /// Error with decoding from message
    #[error("Error decoding from message")]
    DecodeError(Option<InvalidType>),

    // ...
}