Add `EnableMultipleHttp2Connections` property to `HttpHandlerOptions`

[EngRajabi]

If you activate HTTP/2, it is better to activate the SocketsHttpHandler.EnableMultipleHttp2Connections configuration as well, which gives good results.

Docs

• What is HTTP/2 multiplexing?
• MS Learn | .NET | SocketsHttpHandler.EnableMultipleHttp2Connections Property