I know Discord lets you use custom bot keys to add your bots to your server, is there a tutorial for us to do that with OpenNMT models? Also, is there a tutorial for building a chatbot on a website to chat with our models?
You can use one the servers that OpenNMT provide (see the documentation). Your Discord bot or whatever app you are building can simply send requests to the server.
See for example this tutorial to build a chatbot.