The idea here is to couple the upload of the Gutenberg plugin to the WP.org plugin repo tightly to when a new release is published to GitHub, rather than running it from the local system of whoever's in charge of releasing that version.

Moving parts of the release workflow from locally running scripts to GH actions should overall make the process more easily reproducible, and should free up time and resources required for the release process.

The relevant job needs to be [approved](https://docs.github.com/en/free-pro-team@latest/actions/managing-workflow-runs/reviewing-deployments#approving-or-rejecting-a-job) by a qualified reviewer (i.e. a member of the `gutenberg-core` team). This is to ensure that plugin releases cannot be published by anyone who has commit access to the GitHub repo.