Use tagged releases for deployments

[GraemeWatt]

Currently, the deploy job of the CI builds a Docker image and pushes it to Docker Hub tagged with the 7-character GitHub commit reference. Deployment is made by updating this tag in the Kubernetes configuration. There is a version set to a string like 0.9.4dev20230509 where the last part is the date. The first part 0.9.4 has been unchanged since the early days of the project (October 2016). Usually, I manually update the date in the latter part of this string before deploying, so that I can check that the deployment is successful by inspecting the version displayed in the footer of the hepdata.net home page.

It would be better to switch to proper semantic versioning starting from 1.0.0 and make a GitHub Release for each Docker image intended for deployment in production. This might already be implemented, for example, the ci.yaml file has github.event_name == 'release' in the deploy job, but this should be checked before making the first release.