add data context to message trait

[Kilerd]

add MessageContext, so the message handler can use the app data, like connecting to database, can send MQ message.etc.

struct HelloWorldMessage;

#[async_trait]
impl Message for HelloWorldMessage {
    type Output = String;
    async fn handle(self, messager: Arc<Messager>, context: MessageContext) -> Self::Output {
        let conn = context.get::<DatabasePool>();
        // do something
    }
}