Support SslMasterKeyHandler in NettyServerBuilder

I have a problem with adding SslMasterKeyHandler#newWireSharkSslMasterKeyHandler on the server side. I tried to do this with channelFactory:
```
builder.channelFactory(() -> {
final ServerChannel ch = GrpcUtil.getDefaultServerChannelFactory().newChannel();
final ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(SslMasterKeyHandler.newWireSharkSslMasterKeyHandler());
return ch;
})
```
and later with ProtocolNegotiator:
```
final SslContext sslContext = GrpcSslContexts.configure(sslClientContextBuilder).build();
final io.grpc.netty.ProtocolNegotiator negotiator = ProtocolNegotiators.serverTls(sslContext);
builder.protocolNegotiator(tlsNegotiator(negotiator);
```

In the first case, the setting had no effect. In the second case, the server worked incorrectly (it stopped accepting connections, even without a handler, just with a negotiator wrapper).

What should be the proper implementation?

Start with NettyServerBuilder.channelFactory and protocolNegotiator, then read SslMasterKeyHandler.newWireSharkSslMasterKeyHandler and ProtocolNegotiators.serverTls. Determine the supported integration point for server-side TLS master-key handling; done means the handler works with NettyServerBuilder without preventing the server from accepting connections.

Escrito por el modelo de indexación a partir del texto del issue.