Add retries for _write_logs method in KubernetesPodOperator

[wolfdn]

Description

This PR adds retries using Tenacity to the _write_logs method in KubernetesPodOperator.
Previously, this method was logging Reading of logs interrupted with error ...; will retry. when it encountered an ApiException or HTTPError - but actually it did not retry (maybe the retry logic went missing during some refactoring?).

Apart from adding retries, the behaviour is kept the same: If all retries fail, KubernetesPodOperator will print another warning but then proceed with pod cleanup.

Other changes

• Replace from airflow.utils import timezone with from airflow.sdk import timezone - this was consistently failing for me in pre-push hooks otherwise, I assume this is needed now
• Fix order of mocks in test_async_write_logs_handler_api_exception test

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[jscheffl]

@wolfdn Backcompat tests are failing, can you check these?