Document overriding ``XCom.clear`` for data lifecycle management (#17589)
Document overriding ``XCom.clear`` for data lifecycle management (#17589)

This was added in https://github.com/apache/airflow/pull/17405 but was not documented
nathanielvarona/airflow,cfei18/incubator-airflow,apache/airflow,nathanielvarona/airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,mistercrunch/airflow,apache/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,mistercrunch/airflow,nathanielvarona/airflow,lyft/incubator-airflow,nathanielvarona/airflow,apache/incubator-airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,bolkedebruin/airflow,apache/incubator-airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,apache/airflow,nathanielvarona/airflow,lyft/incubator-airflow,apache/incubator-airflow,apache/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,bolkedebruin/airflow,apache/airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,apache/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow