Deployment smoke tests

We need some tests writing which will check that the hugo build was successful and the site deploys correctly. This will be used as part of a PR workflow before enabling merges to `main` once complete. For example if the tests fail for any reason, merging will be blocked until they pass.

I envisage this taking the form of checking the existence of critical files including configuration files and certain show pages. Then the site will be built (as part of an action most likely), spun up (again as part of the action) and then the smoketests will be performed to ensure the thing is running as expected.