code: public void addProxyServer(ProxyServer proxyServer) {
          proxyServers.add(proxyServer);
          extensionHooks.values().forEach(extHook -> hookProxyServer(extHook, proxyServer));
      }
docs: Adds the given proxy server, to be automatically updated with proxy related listeners.
  
  @param proxyServer the proxy server to add, must not be null.
  @since TODO add version
  @see #removeProxyServer(ProxyServer)