refactor: replace deprecated on_event with lifespan context manager

[VishalDhariwal]

This PR migrates the application's startup logic from the deprecated @app.on_event("startup") decorator to the modern lifespan context manager.
According to the FastAPI 0.93.0+ and Starlette documentation, on_event and app.add_event_handler are now deprecated. The lifespan approach is the recommended way to handle startup and shutdown as it provides a cleaner way to manage the state and shared resources (like database sessions) across the app's lifecycle.

Changes Made
Introduced lifespan logic: Created an asynccontextmanager to encapsulate the database synchronization (sync_env_keys_to_db) and logging.
Modernized App Initialization: Updated the app configuration to use the lifespan parameter.
Improved Error Handling: Added a basic try/except block around the startup routine to ensure initialization failures are logged clearly.

[chimosky]

You should remove the no new line at EOF, you can do so with echo >> filename.

If you view your changes with git diff before making a commit, you'll detect issues like this and can resolve it before committing.

[VishalDhariwal]

"Done! I've added the missing newline at the end of the file. Thank you for the suggestion of echo >> filename and for the tip on using git diff to catch these issues before committing. I'll make sure to include that in my workflow moving forward!"

[AjayBandiwaddar]

Hi, I tested this locally and the lifespan approach works correctly.
The deprecation warning is gone after this change. Hope this helps
with the review!

[VishalDhariwal]

Thanks for testing this locally!
The lifespan implementation has been updated and all previous review comments have been addressed (including the EOF newline fix). Looking forward to your approval.
Thanks!