Introduce a deploy script to match the engineering docs

[kasparsd]

Summary

Fixes #558.

Introduce the npm run deploy script mentioned in the engineering docs to ensure the plugin bundle is always created before the deployment to the WP.org plugin repository.

Checklist

• My pull request is addressing an open issue (please create one otherwise).
• My code is tested and passes existing tests.
• My code follows the Contributing Guidelines (updates are often made to the guidelines, check it out periodically).