AwsAthenaOperator: do not generate ``client_request_token`` if not provided (#20854)
AwsAthenaOperator: do not generate ``client_request_token`` if not provided (#20854)

- According to AWS doc (link provided below), boto3 will autopopulated ClientRequestToken is not provided.
  So it's not necessary to generate it explicitly here
- The current logic means a UUID will be generated when the DAG is being parsed into a DAG object.
  When we check this DAG object, we will see a "random" client_request_token
  This may not be desired (for example in the product my team is running, this is causing issue).

AWS Doc link: https://boto3.amazonaws.com/v1/documentation/api/1.18.0/reference/services/athena.html?highlight=start_query_execution#Athena.Client.start_query_execution
apache/airflow,nathanielvarona/airflow,nathanielvarona/airflow,bolkedebruin/airflow,mistercrunch/airflow,mistercrunch/airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,mistercrunch/airflow,cfei18/incubator-airflow,bolkedebruin/airflow,bolkedebruin/airflow,apache/airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,bolkedebruin/airflow,apache/airflow,lyft/incubator-airflow,lyft/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,apache/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow