Automatically deploy site content as appropriate

[anjackson]

Once the editorial workflow is clear, we could consider keeping the BETA site in sync with the most recent accepted changes to the ukwa-site.

This needs to be compatible with however we implement regularly-updated Target/Collection pages generated by Hugo from source data files.

Using a CI process would mean:

• [x] Install a GitLab runner on BETA, associated with this repo.
• [ ] Move the service stack to an internal GitLab repo that gets mirrors to GitHub.
• [ ] Add GitLab CI/CD hooks that use the BETA runner to refresh the ukwa-site image when it gets updated? Or when the stack is updated?