build: add a script to rebuild on typescript file changes

[zimeg]

Type of change

• New feature
• Documentation

Summary

This PR adds a script to rebuild the app on TypeScript file changes:

$ npm run build:watch

Notes

Used alongside changes of slackapi/slack-cli#310 and slackapi/node-slack-sdk#2474 and the WIP hook defaults of the hooks slackapi/node-slack-sdk#2480 file:

{
  "hooks": {
    "get-hooks": "npx -q --no-install -p @slack/cli-hooks slack-cli-get-hooks"
  },
  "config": {
    "watch": {
      "app": {
        "filter-regex": "\\.js$",
        "paths": ["."]
      }
    }
  }
}

This command can be used separate for a smooth development experience with:

$ slack run

Updates to documentation for noting this pattern with the CLI are saved for pages or follow up elsewhere perhaps later! 📚 ✨

Requirements

• I have ensured the changes I am contributing align with existing patterns and have tested and linted my code
• I've read and agree to the Code of Conduct

[srtaalej]

👏

[zimeg]

@srtaalej Let's make server restarts fast so I will merge this 🚢 💨