Creates tests for the store manager api and its endpoints

[calebrotich]

What does this PR do?

This PR creates the endpoints and the tests for the store manager api

Description of Task to be completed:

Create the following minimum endpoints

Http Method	Endpoint	Functionality
POST	api/v1/auth/signup	Creates a new user account
POST	api/v1/products	Used by the admin to add a new product
POST	api/v1/saleorder	Used by the sale attendant to add a new sale order
GET	api/v1/auth/signin	Authentics and creates a token for the users
GET	api/v1/products/<product_id>	Enables a user to fetch a specific product
GET	api/v1/saleorder/<sale_order_id>	Enables a user to fetch a specific sale order
GET	api/v1/products	Enables a user to fetch all products
GET	api/v1/saleorder	Enables a user to fetch all sale orders

How to manually test

The application can be tested at Heroku in combination with postman
The base Url ishttps://store-manager-api.herokuapp.com/
Append the endpoints listed above to test them specifically
https://store-manager-api.herokuapp.com/api/v1/products , for example, tests POST/GET products

Any background information

Some of the endpoints requires Admin authentication

Relevant story

#161309750