Regarding constants and schedule events there is no example in the documentation you pointed to. However, the documentation of the Mendix Docker buildpack explains how to set them in a docker container. You only have to respect the convention, e.g. MX_, and define the variables as any other in the Kubernetes yaml file.
There is no best practises guide at this moment, but Configmaps can be a valid approach when you need to configure a set of pods with a specific environment variable collection. We will take into consideration your feedback to improve the documentation in that regard.
I hope this information is useful.