Implement an event-based API to handle Copilot requests

[alexisabril]

Similar to Octokit's webhook helpers, it could improve the quality of life for developers if incoming requests were parsed uniformly.

[gr2m]

I started speccing out what I think you (and I) have in mind, please let me know:
https://github.com/copilot-extensions/preview-sdk.js/blob/main/dreamcode.md#api

tl;dr:

import { createServer } from "http";
import {
  CopilotExtension,
  createNodeMiddleware,
} from "@octokit/copilot-extension";

const copilotExtension = new CopilotExtension({
  agent: "my-app-name"
});

copilotExtension.on(
  "message",
  async ({ message, octokit, prompt, respond, log }) => {
    await respond.text(`Hi!`);
  }
);

createServer(createNodeMiddleware(copilotExtension)).listen(3000);

The node middleware will be compatible with express' middleware API

[alexisabril]

@gr2m, what would be the purpose for instantiating CopilotExtension with { agent: 'my-app-name' }? Wouldn't the receiver be agnostic?

[gr2m]

oops that should have been

  userAgent: "my-app-name"

(the value for the user-agent header. It should be unique per GitHub App. I'll update the dreamcode)

The userAgent value will be used for all requests made towards GitHub's API and CAPI. Does that make sense?