Enforce running containers as non-root user by default

https://docs.bitnami.com/tutorials/production-ready-charts/#use-non-root-containers

In order to make your Helm chart work with non-root containers, add the securityContext section to your yaml files.

e.g.

```
spec:
  {{- if .Values.securityContext.enabled }}
  securityContext:
    fsGroup: {{ .Values.securityContext.fsGroup }}
  {{- end }}
```