Chart: fix default args/command for databaseCleanup

[Aakcht]

This PR aligns default databaseCleanup command/args with other containers like cleanup https://github.com/apache/airflow/blob/main/chart/values.yaml#L3314 (and all other airflow containers). Having bash overriding default image entrypoint results in inconsistent behavior and causes issues when running airflow under custom user.

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[jscheffl]

Merge after 1.20.0 release please

[potiuk]

@Aakcht This PR has been converted to draft because it does not yet meet our Pull Request quality criteria.

Issues found:

• ❌ Other failing CI checks: Failing: Mergeable. Run prek run --from-ref main locally to reproduce. See static checks docs.

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