fix: dereference jsonschema from a template

[tumido]

Description of the change

Relocates values.schema.json to values.schema.tmpl.json. This file can be templated by Jinja2 and can contain $refs. This file is later processed by pre-commit: it renders the template and unpacks the references.

Existing or Associated Issue(s)

Resolves: #64
Workaround for: https://issues.redhat.com/browse/ODC-7324 (won't be fixed in OCP)

Additional Information

I chose to write this small action in Python since it's native to pre-commit (therefore we're not introducing new stack, instead reusing what's available). It's easy to automate this through pre-commit to ensure our values.schema.json always matches values.schema.tmpl.json recipe. And also it also a very short script compared to golang or js. I know we're introducing a different templating language than used in Helm or helm-docs, it's unfortunate.

You can verify this change by installing this chart from a custom repository:

apiVersion: helm.openshift.io/v1beta1
kind: ProjectHelmChartRepository
metadata:
  name: test-repo
spec:
  connectionConfig:
    url: 'https://raw.githubusercontent.com/tumido/helm-backstage/test-repo'

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the values.yaml and added to the README.md. The helm-docs utility can be used to generate the necessary content. Use helm-docs --dry-run to preview the content.
• JSON Schema generated.
• List tests pass for Chart using the Chart Testing tool and the ct lint command.

[schultzp2020]

LGTM

[sabre1041]

This looks good. Made one small enhancement so that the output is formatted