Wire up SQLAlchemy to create/get/delete a record from the API

[Sybrand]

Describe the task Wire up SQLAlchemy to create/update/get/delete a record (a simple employee record) from the API.

This will serve as an example for how we will be using ORM in the API.

Acceptance Criteria

• [x] Conforms closely to fastapi tutorial: https://fastapi.tiangolo.com/tutorial/sql-databases
• [x] crud.py - contains code to create/update/delete/get record.
• [x] database.py - contains code to connect to db and handle sessions etc.
• [x] schemas.py - schemas modified to work with models as defined in models.py
• [x] main.py - has endpoints for CRUD of record

[ghost]

Added endpoints and supporting crud functions for managing basic employee. Also added test case as part of unit testing.