Add helm schema and supporting actions (version 1.8.0)

[MaikuMori]

Helm tooling is all over the place. I'm adding experimental schema generation via helm-tool. In theory, we could also replace helm-docs with helm-tool, but that would require rewriting the comments. I'm not opposed to this, but let's get the schema working first.

There is also https://github.com/losisin/helm-values-schema-json which has some cool features like custom validation from comments, but I dislike the inline comment style and having to duplicate the description if we want to have both helm-docs and their schema generation.

The current implementation using helm-tool has the downside of descriptions in the schema being prefixed with helm-docs -- prefix.

Other than that, I'm looking forward to helm-tool updates, and maybe we can switch to using just that for everything.

I'm going to keep this open for a bit for potential feedback or additional changes that could be pushed in the 1.8.0 release.

Tasks:

• I've made changes
• I've bumped chart's version in Chart.yaml
• I've added changes to charts CHANGELOG.md
• I've run helm-docs