Make cleanup-pods cronjob conditional on kubernetes executor

[ronaldorcampos]

When trying to run cleanup cronjob on a CeleryExecutor, the cronjob errors when trying to exec airflow kubernetes:

airflow command error: argument GROUP_OR_COMMAND: invalid choice: 'kubernetes' (choose from api-server, assets, backfill, celery, cheat-sheet, config, connections, dag-processor, dags, db, db-manager, fab-db, info, jobs, kerberos, permissions-cleanup, plugins, pools, providers, roles, rotate-fernet-key, scheduler, standalone, sync-perm, tasks, triggerer, users, variables, version), see help above.
Usage: airflow [-h] GROUP_OR_COMMAND ...
....
Options:
  -h, --help            show this help message and exit
stream closed: EOF for airflow/airflow-cleanup-29401785-bq5zs (airflow-cleanup-pods)

Once KubernetesExecutor is enabled, the error above goes away and the cronjob runs to completion.

This PR makes it so the cronjob and its respective service account become conditional on KubernetesExecutor.

Also removed the sidecar.istio.io/inject: "false" from cleanup-pods as requested in #58155 (comment)

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[ronaldorcampos]

Seems we have an issue open about this #46978

[jscheffl]

Thanks for the fix!