CLI: listing all operators set used in the dag

[Xiroo]

I have bumped airflow version(provider, helm chart ...) and had to check all operators if they have breaking changes.
It was too hard to find operators used in the dag with Find all feature of IDE.

I though it would be much better that I can list all operators by cli.
So I want to implement an airflow command line that listing the all operators in the dag files using DagBag or DagModel.

The command will be like following.

airflow operators list

• listing all operators set that caught in the dag processor

airflow operators list --dag-id [dag_id]

• listing all operators set in a dag