SQLALCHEMY_TRACK_MODIFICATIONS - Deprecation warning.

[karlcow]

@laghee I wonder if we will need to do something about this at a point.

 Mar 08 03:11:15 webcompat-metrics app/api Starting process with command `python3 bin/get_count.py needsdiagnosis` by user [email protected]
Mar 08 03:11:20 webcompat-metrics heroku/scheduler.8981 Starting process with command `python3 bin/get_count.py needsdiagnosis`
Mar 08 03:11:21 webcompat-metrics heroku/scheduler.8981 State changed from starting to up
Mar 08 03:11:25 webcompat-metrics app/scheduler.8981 /app/.heroku/python/lib/python3.9/site-packages/flask_sqlalchemy/__init__.py:833: FSADeprecationWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future.  Set it to True or False to suppress this warning.
Mar 08 03:11:25 webcompat-metrics app/scheduler.8981   warnings.warn(FSADeprecationWarning(
Mar 08 03:11:26 webcompat-metrics app/scheduler.8981 (2021-03-08  03:11:25 +0000) INFO: Successfully wrote MILESTONE needsdiagnosis count for 2021-03-08T03:11:24Z to IssuesCount table.
Mar 08 03:11:26 webcompat-metrics heroku/scheduler.8981 Process exited with status 0
Mar 08 03:11:26 webcompat-metrics heroku/scheduler.8981 State changed from up to complete

https://stackoverflow.com/questions/33738467/how-do-i-know-if-i-can-disable-sqlalchemy-track-modifications/33790196#33790196
And pallets-eco/flask-sqlalchemy#351