Allow extending the new HttpContext in HttpConnectionDispatcher

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

The code already has a nice comment for the scenario

https://github.com/dotnet/aspnetcore/blob/v10.0.5/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs#L754-L755

I have a request pipeline that places a couple of features in the `HttpContext`, but within a SignalR method, these are not available on the one you get from `Context.GetHttpContext()`. As a workaround, I have placed the relevant data on the `.Items` instead, but it would've been great, if I was able to centrally control the creation of the new `HttpContext`.

### Describe the solution you'd like

As mentioned in the comment: A configurable callback, allowing me to extend what's available in the new `HttpContext`

### Additional context

_No response_