Improve Docstring for AWS Athena Hook/Operator

[amariucaitheodor]

closes: #10575
related: #10575

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contribution Guide (https://github.com/apache/airflow/blob/master/CONTRIBUTING.rst)
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[XD-DENG]

Thanks @theodor1289 . I updated the PR subject a little bit, hope you don't mind

[boring-cyborg]

Awesome work, congrats on your first merged pull request!