Write a YAML spec that can validate nebula config files

[jasikpark]

JSON Schemas can be applied to YAML documents, allowing documentation and validation of configuration files in editors that consume those specs.

It could be helpful to add a nebula.json file to the https://www.schemastore.org/json/

Refs:

• https://json-schema.org/implementations.html
• https://www.jsonschema.net/
• https://github.com/jy95/docusaurus-json-schema-plugin
• https://jy95.github.io/docusaurus-json-schema-plugin/boxFileSchema
• https://json-schema-everywhere.github.io/yaml