Update Documentation for FastAPISessionMaker and SQLAlchemy Session Management

[sahil-soni18]

This PR improves the documentation for the fastapi_utils.session module, specifically focusing on the usage of the FastAPISessionMaker class for managing SQLAlchemy sessions in FastAPI applications. The key updates include:

• Clear and concise explanations of the steps required to configure and use the FastAPISessionMaker class.
• Refined example code to better illustrate the process of defining ORM tables, configuring the database URI, and creating a get_db dependency for session management.
• Updates to ensure best practices are emphasized, particularly regarding session finalization and error handling.
• Removal of repetitive code in the documentation, ensuring that each step is explained with specific parts of the code, rather than the entire code block.

These updates aim to make the process of integrating SQLAlchemy with FastAPI more understandable and approachable for developers.