Add HIP for outputting chart JSON schemas

[remcohaszing]

Helm supports JSON schema validation to validate values.yaml. It would be nice if JSON schema validation is also possible by editors of values.yaml files. It would be nice if JSON schemas can be referenced by dependant Helm chart JSON schemas. Both will be possible if the JSON schemas are served on separate URLs.

It was requested in helm/helm#9920 (comment) to write a HIP.

[technosophos]

As an alternative idea, would it be sufficient if helm show had a schema or values-scheme subcommand that emitted the schema?

[technosophos]

We do have to tell an OCI registries story for this feature as well. That's the main thing that would need to be addressed.

I left a comment already about perhaps considering this as a new subcommand to helm show. There are three reasons I currently prefer that:

1. It is ultimately simpler to implement
2. I don't see a clear way to make this work with OCI registries, which are being considered as the default chart serving mechanism for v4.
3. We have had very bad luck getting package providers to upload .prov files, and I am suspicious that we would see the same thing here, which would reduce the usefulness. Further, it means that a repo that doesn't support this feature becomes a blocker for all of the users who would want this feature.

In contrast, using a local command would enable devs to generate this information as desired, while still allowing repo admins to choose to generate and serve schemata as static assets in a well-known location.

[technosophos]

This implies that chart publishers will publish schema files, but it does not explain how charts stored in OCI registries would make schemata available. While OCI is considered an experimental feature, because it is part of Helm's core we would need to introduce a solution for that registry as well as for a regular Helm chart repo.