Allow customization of Netty Bootstrap and ChannelPipeline

[kevinherron]

This allows e.g. a SOCKS proxy to be configured fairly easily:

public static void main(String[] args) throws UaException {
  var client = OpcUaClient.create(
      "opc.tcp://milo.digitalpetri.com:62541/milo",
      endpoints -> endpoints.stream()
          .filter(e -> Objects.equals(e.getSecurityPolicyUri(), SecurityPolicy.None.getUri()))
          .findFirst(),
      tcb -> tcb.setChannelPipelineCustomizer(p -> addSocksProxyHandler(p)),
      ccb -> {}
  );

  client.connect();
}

private static void addSocksProxyHandler(ChannelPipeline pipeline) {
  var handler = new Socks5ProxyHandler(new InetSocketAddress("localhost", 1080));
  pipeline.addFirst(handler);
}