Update changelog for changes since 2.2.0b2 (#18639)
Update changelog for changes since 2.2.0b2 (#18639)

This updates the changelog for commits up to and including 840ea3efb
bolkedebruin/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,apache/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,lyft/incubator-airflow,nathanielvarona/airflow,lyft/incubator-airflow,mistercrunch/airflow,danielvdende/incubator-airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,apache/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,mistercrunch/airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,apache/airflow,cfei18/incubator-airflow,apache/airflow,lyft/incubator-airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,bolkedebruin/airflow,apache/airflow,cfei18/incubator-airflow,lyft/incubator-airflow,mistercrunch/airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,bolkedebruin/airflow,apache/incubator-airflow