additionalProperties not rendered

[m-mohr]

In schemata for objects it is allowed to set additionalProperties to true and allow arbitrary key-value pairs. Unfortunately this is not rendered by ReDoc and users reading the rendered documentation are not aware of the fact that they can add more properties than the one specified directly in the OpenAPI specification.

Example:

openapi: 3.0.1
info:
  title: Test
  version: "0.1.0"
paths:
  /example:
    get:
      summary: Example operation
      description: This is a simple example.
      responses:
        '200':
          description: This is a sample schema for a response with additionalProperties.
          content:
            application/json:
              schema:
                type: object
                properties:
                  id:
                    type: number
                  stringProperties:
                    type: object
                    additionalProperties:
                      type: string
                  untypedProperties:
                    type: object
                    additionalProperties: true
              example:
                id: 123
                stringProperties:
                  anotherProp: "test"
                untypedProperties:
                  anotherProp: "test"

Rendered as: https://rebilly.github.io/ReDoc/?url=http://mamo-net.de/feature/redoc/additionalprops.yaml

I would expect that additional properties of any type are allowed for the untypedProperties object. Should be the same way as for the stringProperties.

[m-mohr]

@RomanGotsiy Created a PR (#597) to solve this issue.