[Schema] TypeScript to JSON Schema

[kjdelisle]

Story

As a LB4 dev, I want my TypeScript classes to be automatically converted into JSON Schema so that I have a metadata representation of my classes that I can freely convert into other formats (OpenAPI schema, other classes in other languages, etc)

Cross-posting from #700:

In our Todo model example, we are duplicating information about model properties - first time in Model definition, second time in Swagger (OpenAPI) Schema.

We should have a helper function that can create Swagger/OpenAPI Schema from the Model data.

Acceptance Criteria

• Create a metadata type system (yikes!) that leverages the existing decorator names (@model, @property)
• For @property:
  • Introspect the type of the property, either as a primitive type, or otherwise
    • For complex types, mark with $ref (we can dereference this later)
• For @model:
  • Add top-level specific metadata to the entry for this type:
    • description
    • title
    • required
    • oneOf (it's a union type!) not supported by current juggler implementation
• Write a blog post about how awesome this will be (unless it's not, then don't ;) )
• Document on loopback.io