[SignalR] Precision on specifications for MessagePack

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Describe the bug

Hi,
I try to create a lib to communicate with SignalR from an Arduino ([ESP32S2 Saola](https://docs.espressif.com/projects/esp-idf/en/latest/esp32s2/hw-reference/esp32s2/user-guide-saola-1-v1.2.html) to be precise) and I'm using [HubProtocol.md](https://github.com/dotnet/aspnetcore/blob/main/src/SignalR/docs/specs/HubProtocol.md) as reference for my dev.

As Arduino is a very limited device, I want to use MessagePack as serialization and websocket as transport but I've 2 "issues".

1) The HandshakeResponse is sended in binary and not in text

It's not really an issue, I can manage a response in binary but in [TransportProtocols.md](https://github.com/dotnet/aspnetcore/blob/main/src/SignalR/docs/specs/TransportProtocols.md) it is specified this "When using a text-based protocol like JSON, it is preferable for the WebSockets transport to use Text frames.". As Handshake is always in json, I've waited for a response in text. Maybe, it's a good idea to specify in the document that when using MessagePack, the reponse will be in binary.

2) In regular frame after Handshake, I have 1 unspecified byte more in frame

I've verified with Wireshark the problem :

At the end of the payload, 0x82 0x03 is a correct websocket header that specify a binary frame with 3 bytes of payload and 0x91 0x06 is a valid Ping message but what is 0x02 ? I have checked the whole documentation and nowhere it's specified a header or something else between the websocket header and the message. For reference, I quote the Ping message specification :


### Expected Behavior

Suppression of the "unwanted" byte or a modification of the specification to tell what is this byte to be able to write a conform client

### Steps To Reproduce

My test program (on C# side) is very simple, 1 aspnet core project with 1 SignalR hub:

Program.cs:
```csharp
namespace Arduino.SignalR.Client.DemoServer
{
public class Program
{
public static void Main(string[] args)
{
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSignalR().AddMessagePackProtocol();

var app = builder.Build();

app.MapHub("/TestHub");

app.Run();
}
}
}
```

TestHub.cs:
```csharp
using Microsoft.AspNetCore.SignalR;

namespace Arduino.SignalR.Client.DemoServer
{
public class TestHub : Hub
{
public async Task EchoMessage(string message)
{
await Clients.All.SendAsync("ReceivedMessage", message);
}
}
}
```

The Arduino side is a little more complexe and could be find here [Arduino.SignalR.Client](https://github.com/EscapeAutomate/Arduino.SignalR.Client). It's a WIP :)

### Exceptions (if any)

_No response_

### .NET Version

6.0.400

### Anything else?

ASP.NET Core version: 6.0
IDE: Visual studio for C# and Cpp

```
dotnet --info
.NET SDK (reflecting any global.json):
Version: 6.0.400
Commit: 7771abd614

Environnement d'exécution :
OS Name: Windows
OS Version: 10.0.19044
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\6.0.400\

global.json file:
Not found

Host:
Version: 6.0.8
Architecture: x64
Commit: 55fb7ef977

.NET SDKs installed:
2.2.207 [C:\Program Files\dotnet\sdk]
3.1.422 [C:\Program Files\dotnet\sdk]
5.0.303 [C:\Program Files\dotnet\sdk]
5.0.408 [C:\Program Files\dotnet\sdk]
6.0.202 [C:\Program Files\dotnet\sdk]
6.0.203 [C:\Program Files\dotnet\sdk]
6.0.303 [C:\Program Files\dotnet\sdk]
6.0.400 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.28 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.28 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

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```