Fix howto guide link in AzureBlobStorageToS3Operator docstring

[o-nikolas]

The reference pointed at the AzureBlobStorageToGCSOperator label, which resolves to the Google provider's Azure Blob to GCS guide, so readers following the "how to use this operator" link landed on the docs for a different transfer entirely.

---

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

---

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.