In Airflow 2.0 we should remove the ability to add operators and hooks via plugins.

I think we should deprecate adding Operators and Hooks via the Airflow plugin mechanism.

I think plugins should be reserved for any mechanism that a plain-ol python module import won't work for (which is basically anything that needs to tie deeply in to the Webserver or Scheduler process).

To that end I think we should deprecate adding operators via plugins:

    from airflow.operators.my_plugin import MyOperator

can become

    from my_plugin import MyOperator

with no impact on functionality.

For this not to be a hard/sudden breaking change we should issue a deprecation warning for this in 1.10.12 - #9500

Discussed here:

https://lists.apache.org/thread.html/a1453d6a6f113709386b61c68c3f5cd61b258fe78f07811169500fe3%40%3Cdev.airflow.apache.org%3E