Adding support for custom vocabularies

[thomascobb]

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