feat: Support for StatefulSets, DaemonSets and Headless Services

[davidkim83]

Changes

• enhanced the deployment template to accommodate variations between Deployment/StatefulSet/DaemonSet
• created a new template for headless Service to accompany StatefulSet
• HPA and VPA now reflects the deployment.kind
• added/edited test cases to cover the above changes
• updated docs to increase scope of chart (no longer 'stateless-only')

Closes

#319

Remarks

• The idea of changing the top attribute from deployment to workload was discarded as it is deemed too intrusive.

[rasheedamir]

Thanks for the PR @davidkim83

@aslafy-z what is your opinion on supporting statefulsets, daemonsets, etc. in this chart? the original idea with this chart has been for stateless applications only

[davidkim83]

@rasheedamir my pleasure!

Please check this comment where @aslafy-z already gave his opinion, but I won't stop you from reconfirming :)

FWIW, this chart already supports Jobs & CronJobs. It would gain so much potential from supporting other types of long-running workloads.

I had also thought of separate top-level attributes (such as statefulset: and daemonset:, but then the chart would no longer be application, but applications. I think it's good that the chart remains limited to deploying a singular workload, and not many.