Added inventory app with models, views, serializers, tests and custom_auth

[Imotechs]

Description

This pull request includes the following updates:

• app.settings FILE:
  --registered new app inventory, rest_framework and rest_framework_simplejwt', -- changed DATABASES to use Postgresql`
  -- added REST_FRAMEWORK list of permission and auth classes
  -- added an additional AUTHENTICATION_BACKENDS to the default django own
  -- added SIMPLE_JWT list for JWT Authentication and logics

• Inventory App:
  -- I created a new app called inventory

  • Models: Added Product, Category, Order, and OrderItem models in inventory app.
  • Views: Implemented views for CRUD operations on Product, Category, Order, and OrderItem.
  • Serializers: Created serializers for the Product, Category, Order, and OrderItem and User models.

• File: I Added custom_auth, in the inventory app for
  Custom Authentication handling both user email and name on login.

• Tests:

  • Added unit tests for views in the inventory app to ensure proper functionality.

How i Tested my Codes

• I Ran the test suite using python manage.py test and verified that all tests pass.

Also know that

• My codes follows the style guidelines of this project as describe in README.md

• I have performed a self-review of my own code

• I have commented my code where neccessary

• My unit tests pass locally with 0 Errors