Services: Add a WebSocket service

The WebSocket service isolates communication with a WebSocket to its
own isolated process. Similar to other isolating services, it has its
own user and group.

Userland/Libraries/LibWebSocket/WebSocket.cpp

@@ -559,6 +559,9 @@ void WebSocket::discard_connection()
 {
     VERIFY(m_impl);
     m_impl->discard_connection();
+    m_impl->on_connection_error = nullptr;
+    m_impl->on_connected = nullptr;
+    m_impl->on_ready_to_read = nullptr;
     m_impl = nullptr;
 }