Fix: Client websocket connection hangs when server disconnects (#657)

```
_, err := io.Copy(src, dst)
```
io.Copy doesn't automatically fail when `src` connection closes. 

This change guarantees that when at least connection fails (either src,
dst) the other one also disconnects

pkg/abstractions/endpoint/buffer.go

@@ -558,6 +558,11 @@ func (rb *RequestBuffer) proxyWebsocketConnection(r *request, c container, diale
 }
 
 func forwardWSConn(src net.Conn, dst net.Conn) {
+	defer func() {
+		src.Close()
+		dst.Close()
+	}()
+
 	_, err := io.Copy(src, dst)
 	if err != nil {
 		return