WIP: self-hosted socket mode and http mode

[vegeris]

This PR is being broken out to separate updates for socket mode from HTTP mode

---

Summary

Entrypoints for running Deno apps via an SDK-managed socket connection or via HTTP mode

Testing

Check out this branch. Create a new Deno app via the template (slack-public create --template https://github.com/slack-samples/deno-starter-template) and update the .slack/hooks.json file with the following (socket mode):

{
  "hooks": {
    "get-hooks": "deno run -q --allow-read --allow-net https://deno.land/x/deno_slack_hooks@1.5.0/mod.ts",
    "start": "deno run -q --config=deno.jsonc --allow-read --allow-net --allow-run --allow-env --allow-sys=osRelease file:///Users/evegeris//dev/deno-slack-runtime/src/self-hosted-socket-mode.ts"
  },
  "config": {
    "sdk-managed-connection-enabled": true
  }
}

or with "start": "deno run -q --config=deno.jsonc --allow-read --allow-net --allow-env --allow-sys=osRelease file:///your/filepath/src/self-hosted-http-mode.ts" to test HTTP mode

Run the app in socket mode without the CLI by setting an app token environment variable (export SLACK_APP_TOKEN=... and optionally, export SLACK_BOT_TOKEN=..., export SLACK_API_URL=https://dev.slack.com/api) and running the Deno command directly; deno run -q --config=deno.jsonc --allow-read --allow-net --allow-env --allow-run --allow-sys file:///Users/evegeris//dev/deno-slack-runtime/src/self-hosted-socket-mode.ts

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.