Incorrect documentation preview when template contains a $ref

[rovellipaolo]

When generating a documentation preview locally, with serverless generateDocumentation command, the documentation will not be generated correctly if the template contains a reference to another local model with the $ref keyword.

For example the following template (taken directly from the README.md file):

custom:
  documentation:
    models:
      -
        name: "Customer"
        description: "This is a customer"
        contentType: "application/json"
        schema:
          type: "object"
          properties:
            name:
              type: "string"
            address:
              $ref: "{{model: Address}}"

will generate the following documentation preview:

"components": {
  "schemas": {
    "Customer": {
      "type": "object",
      "properties": {
        "name": {
          "type": "string"
        },
        "address": {
          "$ref": "{{model: Address}}"
        }
      }
    }
  }
}

As you can see the $ref value is "{{model: Address}}" (wrong) rather than "#/components/schemas/Address" (correct).

NOTE: The documentation preview will be generated correctly if the reference is to a URL (e.g., "http://path/to/your/resource").

Although it's expected that the documentation preview might potentially be invalid or anyway different from the final documentation (which is why it's called "preview"), it would be nice to fix this use-case.