Add support for jsonschema export similar to openapi-v3

[peschmae]

Describe the problem/challenge you have
Most text editors use json schema, to autocomplete and validate YAML files. To make it easier to the users, to write YAML files based on a YTT schema, it would be great to have a way to create the json schema from a YTT file, similar to the openapi schema that is currently implemented.

Describe the solution you'd like
Support for json schema as a output option for ytt -f schema.yaml --data-values-schema-inspect --output

Anything else you would like to add:
During kubecon 2024, the talk Developers demand UX for K8s highlighted that YAML validation & auto-completion seems to be one of the main struggles developers face when working with Kubernetes.

Using YTT and it's schemas, could help alleviate that issue.

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[peschmae]

After diggin in to the openapi schema generation for #897 I think this shouldn't be too hard to implement, as the property attributes are mostly identical, and a lot of the code could be reused.

From a quick glance at https://swagger.io/docs/specification/data-models/keywords/ the biggest difference is that type is a list, and nullable isn't an attribute, but needs to be added to the type list.

@prembhaskal Let me know if I should draft a pull request for this.

[peschmae]

I found some time today, and threw a quick and dirty approach together in a feature branch: https://github.com/peschmae/ytt/tree/feat/jsonschema

It would still need a refactoring, to reduce duplicate code shared with the openschema export, but it already converts into a valid schema that is properly interpreted by vscode.

[prembhaskal]

@peschmae I am bit stuck with other stuff, but I can review it over weekend. but you can go ahead and put up a PR if you want some early eyes on it.

@100mik @sethiyash PTAL when you get time.

[prembhaskal]

I am unable to check it still, so removed assignee.

[renuy]

@cppforlife @100mik Please take a look at this