Support for multipart-form in API specs rendering

[Anshuman71]

The docs-kit renderer should show at least the payload mime type (multipart-form).

Below is an example spec that can help with the testing of this feature.

/demofiles:
  post:
      description: Upload new files
      body:
          multipart/form-data:
            properties:
              fileName:
                description: Name of the file
                type: string
                required: true
              content:
                description: Content of the file
                type: file
                fileTypes: ['application/octet-stream','image/png']
                required: true
              manifest:
                description: Description of the file
                type: object
                fileTypes: ['application/json']
                required: true
      responses:
        200:
          body:
            application/json:
              type: object