Fixes date command in breeze build-image to work on MacOS (#14458)
Fixes date command in breeze build-image to work on MacOS (#14458)

The `date` command on MacOS does not have --rfc* flags so we have
to replace the flag with manually crafted rfc-compliant date.

Fixes #14393
lyft/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,lyft/incubator-airflow,apache/incubator-airflow,lyft/incubator-airflow,bolkedebruin/airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,dhuang/incubator-airflow,mistercrunch/airflow,danielvdende/incubator-airflow,apache/airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,apache/airflow,lyft/incubator-airflow,dhuang/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,bolkedebruin/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,apache/airflow,apache/incubator-airflow,mistercrunch/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,apache/airflow,bolkedebruin/airflow,sekikn/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,apache/incubator-airflow,bolkedebruin/airflow,sekikn/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,apache/airflow