Patch sql_alchemy_conn if old Postgres schemes used

[slyapustin]

This PR fixed the unsupported postgres:// schema since SQLAlchemy 1.4.

It's an enhanced version of #22333.

It's specifically fixed an issue with Heroku default Postgres URI:
https://help.heroku.com/ZKNTJQSK/why-is-sqlalchemy-1-4-x-not-connecting-to-heroku-postgres

This is a blocker for the Airflow Heroku integration at that moment:
https://github.com/slyapustin/airflow-on-heroku

[boring-cyborg]

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[potiuk]

nice!

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[slyapustin]

Thanks for approving PR @potiuk
I just updated it to fix the flake8 issue (long line in the docstring).

[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[potiuk]

Some timeout issues. (we need to fix them soon BTW).

[kaxil]

cc @ephraimbuddy @jedcunningham -- We should include this in 2.3.3