Adding helm chart for grocy

[handyman5]

This PR introduces a new Helm chart for running grocy in Kubernetes:

$ helm upgrade --install grocy chart/ --values=chart/values.yaml
Release "grocy" has been upgraded. Happy Helming!
NAME: grocy
LAST DEPLOYED: Sat Feb 17 23:22:41 2024
NAMESPACE: grocy
STATUS: deployed
REVISION: 5

It primarily uses the default templates and behaviors you get from helm create <name>, with the necessary and appropriate modifications (such as adding both processes into the same pod).

Note that it creates a persistent volume claim for the app data directory, and annotates it such that helm will not delete the volume when the chart is deleted (and it will re-use the volume if you reinstall the chart).