Added Websocket::with_message_stream for client message customization

[D1plo1d]

This PR adds a Websocket::with_message_stream() in order to allow developers to customize the ClientMessages received by their Websocket.

Specifically, Websocket::with_message_stream() can be used to implement file uploads over websockets as well as websocket serialization alternatives such as msgpack.*

* Note: At the moment a developer implementing a msgpack websockets would need to convert their serialization errors to serde_json::error. This is less ergonomic then ideal but it is hoped that it is workable as a first API iteration.

Primary Motivation

Enable developers to explore uploading files over non-HTTP channels.

Secondary Motiviation

Allows other ClientMessage customizations.

API Changes

• Added Websocket::with_message_stream() to allow developers to customize the ClientMessage creation for their websocket.
• Exposed ClientMessage as pub (for Websocket::with_message_stream)
• Added ClientMessage::from_bytes() to keep code duplication at a minimum

Example Usage

struct FutureProtocol {
    msg: Vec<u8>,
    uploads: UploadValue,
}

let message_stream = message_stream.map(|msg: FutureProtocol| {
    let mut client_message = ClientMessage::from_bytes(msg.payload)?;

    if let ClientMessage::Start {
        payload: request,
        ..
    } = &mut client_message {
        request.uploads = msg.uploads;
    }

    Ok(client_message)
});

let connection = async_graphql::http::WebSocket::with_message_stream(
    schema,
    message_stream,
    initializer,
    async_graphql::http::WebSocketProtocols::GraphQLWS,
)

Example usage in an application: https://github.com/tegapp/teg/blob/develop/crates/server/src/main.rs

[sunli829]

Thank you, this PR looks great! 😁