Adding support for custom vocabularies

Is your enhancement related to a problem? Please describe.

I would like to use VSCode-YAML to edit a file where one of the properties is an enum whose value must appear as another property in the same document. An example of the file I would like to edit is here: https://github.com/json-schema-org/json-schema-spec/issues/706

After much searching on the JSON schema github site, most of the closed issues are around the rejected $data idea. It appears that the accepted way to do this is with a custom vocabulary: https://github.com/json-schema-org/json-schema-vocabularies

There is one particular vocabulary that would implement this validation: https://gregsdennis.github.io/json-everything/usage/vocabs-data.html

It has a C# reference implementation, but not a JS one.

Describe the solution you would like

To know what plans VSCode-YAML has for supporting custom vocabularies, either natively or via an extension, and to implement this particular one.

Describe alternatives you have considered

I considered writing an extension to just handle my use-case, but thought I'd ask to see if anyone had thought about custom vocabularies in general

Start with the VSCode-YAML repository and the linked JSON Schema custom-vocabulary and json-everything documentation. Compare the requested same-document enum validation with the project's current support, then determine whether native support or an extension is the intended scope. Done means an agreed implementation path or support for the cited vocabulary, with validation demonstrated on the example document.