Temp/Add mock routes for city score and air quality score

[danoand]

Files Modified:

• app/ml.py

Details:

1. Add a mock route for fetching the overall city score /city_scr/...
2. Add a mock route for fetching a city's air quality score /air_qual_scr/...
3. Insert docstring comments for the eventual business logic to be coded

[danoand]

@PalmerTurley34 hey... if you don't mind please go ahead and review/approve this PR. Merging it will enable us to:

• have the web team use the FastAPI as their DS backend rather than the mock web service we have deployed on Digital Ocean (another PaaS like AWS)
• all the routes we agreed upon will be in the FastAPI code - with these routes being mocked out routes
• give me time to build out the real city score and air quality routes but not block the web team

[danoand]

Closing this PR and will create a new PR with these code changes