[Backend] Added Class methods to User Model

[amlannandy]

Description

Added various class methods to reduce repeated code in the user routes.

1. Method for converting user model into json format
2. Method to match user input password with actual hashed password of that user.
3. Moved the password hashing process from the routes to the Class constructor

Fixes #103

Type of change

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Try testing login, create user, get profile and get user by id routes

Test Configuration:

• Windows 10
• Postman

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules