Code generation fails if `ref` does not start with `#/definitions/`

Currently code generation for some schemas is failing due to `ref` not starting with `#/definitions/`. Here is where the error is being thrown: https://github.com/cdklabs/json2jsii/blob/main/src/type-generator.ts#L514-L518

Here are some examples of schemas that are failing with this,
* https://github.com/vinayak-kukreja/SchemaValidation/blob/main/chart-schemas/dagster.json#L546-L551
* https://github.com/vinayak-kukreja/SchemaValidation/blob/main/chart-schemas/nginx-ingress.json#L45-L50