otelmux middleware doesn't support websockets

[koschos]

Description

otelmux middleware doesn't support websockets.

Environment

• OS: [all]
• Architecture: [all]
• Go Version: [all]
• otelmux version: [all]

Steps To Reproduce

1. Use this middleware with websockets
2. Run ...
3. See error Unexpected error upgrading connection, error type assertion failed ResponseWriter not a Hijacker

Expected behavior

Middleware supports websockets

The method below must be added in the file mux.go

func (h *recordingResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	if hijacker, ok := h.writer.(http.Hijacker); ok {
		return hijacker.Hijack()
	}
	return nil, nil, fmt.Errorf("underlying ResponseWriter does not support hijacking")
}