Refactor shopcarts to use Flask-RESTX

[nyu-kaitlyn]

As a developer I need to refactor the shopcarts application to use Flask-RESTX So that I can take advantage of its powerful features and simplify the development process

Details and Assumptions

• The existing shopcarts application is built in Flask and needs to be updated to use Flask-RESTX

  Acceptance Criteria

  Given an existing shopcarts application built on Flask
  When I refactor the code to use Flask-RESTX
  Then I can take advantage of features such as automatic Swagger documentation, built-in validation and serialization, and simplified route definition, resulting in faster development times and improved maintainability of the codebase

[nyu-kaitlyn]

More detail:

• Refactor your micro service to use Flask-RESTX following the file layout outlined in lab-flask-restplus-swagger.
• Make sure that all HTTP errors return json error messages and not html (note: You will actually be able to delete most of the error_handlers.py file because Flask-RESTX will handle most of these errors for you).
• Run your test cases and make sure that your Flask-RESTX implementation still works like the original.