Add Swagger Annotations to all WishlistItem endpoints to convert API into RestX-Swagger manner

[tzuanwang]

As a developer I need to add Swagger annotations to wishlist item endpoints So that the REST APIs for WishlistItems are documented and accessible at /apidocs, and api endpoints are located under /api

Details and Assumptions

• Swagger annotations will be added to the Flask-RESTX endpoints
• Annotation examples:

  @api.doc("update_pets", security="apikey")
  @api.response(404, "Pet not found")
  @api.response(400, "The posted Pet data was not valid")
  @api.expect(pet_model)
  @api.marshal_with(pet_model)

• The Swagger UI will be accessible at /apidocs/
• The api endpoints will be relocated to /api/...

• Jsonify should be removed, and the error message will be converted to json by restx

  Acceptance Criteria

  Given the microservice using Flask-RESTX
  When I visit endpoints at /api/...
  Then the wishlistItem APIs work fine like before
  When I test with errors on purpose
  Then the error message will be in json format
  When I visit Swagger documentations at /apidocs
  Then all the API documentation for wishlistItem should be available.