Deferrable operators doc clarification (#20150)
Deferrable operators doc clarification (#20150)



The language "when two tasks defer based on the same trigger" is a bit confusing. Many tasks can reuse the same trigger class.  But two tasks can't defer using the same trigger _instance_. I think what's important to call out here, and what I try to make clearer, is that the exact same instance of the trigger may have multiple copies of itself running.

Additionally I clarify cleanup is not _only_ called "when this happens" (that is, when trigger is "suddenly removed"), but called every time the trigger instance exits, no matter the reason.
cfei18/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,apache/airflow,bolkedebruin/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,apache/airflow,mistercrunch/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,bolkedebruin/airflow,bolkedebruin/airflow,bolkedebruin/airflow,mistercrunch/airflow,apache/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,mistercrunch/airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,cfei18/incubator-airflow,apache/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow