Procedure for monthly routine maintenance

We should document how to do routine maintenance. I can think of a few things to do:

- Check whether we are using Kubernetes alpha/beta API versions, and upgrade them if so (after checking the upgrade notes).
- Check whether the Kubernetes cluster has an upgrade available, and upgrade if so (after checking the upgrade notes).
- Check whether the Nginx minor version is still supported, and upgrade it if not (after checking the upgrade notes).

Start by reviewing the repository's current Kubernetes and Nginx configuration, then consult the relevant upgrade notes and support information. Document a repeatable monthly procedure covering deprecated Kubernetes API versions, available cluster upgrades, and Nginx minor-version support, including the checks and upgrade guidance.

Written by the indexing model from the issue text.