docs: add automated remediation guardrails to retry docs

[vividbaek]

Add a short section to the Dag-level retry how-to describing guardrails for automated remediation Dags.

The new section clarifies that pools can limit concurrent recovery work, but they do not limit how often the same recovery action is attempted across Dag runs. It also suggests using small cooldown markers and maximum automatic action counts before requiring manual review.

The section includes a caveat that Airflow Variables may be sufficient for small guard values, but should not be used as a high-volume state store or as a strongly consistent locking mechanism.

This is a documentation-only change. No runtime behavior is affected.

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

• Yes — GLM 5.1

Generated-by: GLM 5.1 following the guidelines

[potiuk]

@vividbaek A few things need addressing before review — see our Pull Request quality criteria.

• ❌ Build docs. See docs.

No rush.

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Note: This comment was drafted by an AI-assisted triage tool and may contain mistakes. Once you have addressed the points above, an Apache Airflow maintainer — a real person — will take the next look at your PR. We use this two-stage triage process so that our maintainers' limited time is spent where it matters most: the conversation with you.

[vividbaek]

Sorry for the confusion, and apologies for not checking this more carefully earlier.
I re-ran the docs spellcheck locally with ANSWER=n breeze build-docs apache-airflow --spellcheck-only --one-pass-only, added cooldown to spelling_wordlist.txt, and the build now passes.
The earlier failure was due to the spellchecker word list, not the docs change itself. Please re-run CI.