Add more fields to Chart.yaml

[batpad]

We should add some more useful fields to the Chart.yaml as per https://helm.sh/docs/topics/charts/#the-chartyaml-file

Some things are descriptive, like maintainers and sources -- some like appVersion we should decide on how we want to handle versioning / publishing stable versions, etc.

Just filing this as a stub ticket so we remember to do at some point.

cc @geohacker @Rub21