`serve_logs` cannot depend upon the FAB provider

[ashb]

Originally posted #48457 (comment)

The move of serve_logs to FAB is not right @potiuk @vincbeck .

Serve logs is called automatically by the celery executor, which means that Celery worker now will not run without FAB installed.

Even worse, it's called in the same way by the triggerer and the scheduler (at least with LocalExecutor).

FAB != Flask. Serve logs should not have been moved like this. Any chance either of you can fix this before we were hoping to cut the RC2 tomorrow?

[ashb]

If someone is feeling adventurous we could replace gunicorn and flask with starlette and unicorn.

Or we can just add back in the dep on flask and gunicornto airflow-core for now

[potiuk]

Indeed. Thanlks @ashb for spotting it . My bad - missed this during review . PR on the way,