Add values schema

[wkloucek]

Add a values schema, like eg. #57 tried to do it.

Needed for eg. a OpenShift Helm chart certification (https://redhat-connect.gitbook.io/partner-guide-for-red-hat-openshift-and-container/helm-chart-certification/helm-chart-requirements)

We should find a way to enforce the proper adaption of the schema in future PRs.

[Excds]

I did a bit of research on this and this is certainly not a painless topic. There are unmaintained projects such as https://github.com/karuppiah7890/helm-schema-gen where you can generate a schema file from values, but that will require manual editing of the resulting schema to make things work. And doing things manually completely makes that a moot point for when you have to update values.

Then there's going from the other way around with something like https://github.com/giantswarm/helm-values-gen, but that completely breaks the current documentation setup.

I found some things where both the values and schema would be generated from Yet Another Format.

So, this is currently not actionable without a bigger research task and discussion around how to manage this.

[wkloucek]

I stumbled across this recently: https://github.com/SocialGouv/helm-schema

Probably worth a proof of concept for a few values.

[wkloucek]

There is https://github.com/dadav/helm-schema, too