TUN-7253: Adopt http.ResponseWriter for connection.ResponseWriter

connection/http2.go

@@ -197,6 +197,7 @@ type http2RespWriter struct {
 	flusher       http.Flusher
 	shouldFlush   bool
 	statusWritten bool
+	respHeaders   http.Header
 	log           *zerolog.Logger
 }
 
@@ -276,6 +277,14 @@ func (rp *http2RespWriter) WriteRespHeaders(status int, header http.Header) erro
 	return nil
 }
 
+func (rp *http2RespWriter) Header() http.Header {
+	return rp.respHeaders
+}
+
+func (rp *http2RespWriter) WriteHeader(status int) {
+	rp.WriteRespHeaders(status, rp.respHeaders)
+}
+
 func (rp *http2RespWriter) WriteErrorResponse() bool {
 	if rp.statusWritten {
 		return false