Add support for HAProxy Protocol ("proxy protocol")

Is there a way to add a CustomHandler to ChannelPipeline using NettyServerBuilder ?

I initialize my GrpcNettyServer by below:

```
NettyServerBuilder serverBuilder =
NettyServerBuilder
.forPort(config.getPort())
.addService();
.intercept();
.executor();
.build();
```
All I want is to get the channel from the server and add a custom handler to the channel pipeline.
Does NettyServerBuilder supports that option ?