docs: Add use_off_peak_window attr to aws_opensearch_domain data source

[acwwat]

Description

This is a follow-up PR to add the documentation for the use_off_peak_window attribute to the aws_opensearch_domain data source. The first PR was focused on getting the fix in ASAP, so now I have time to review and update the doc.

Relations

Relates #36291

References

Referred to #36067 for the same attribute description.

Output from Acceptance Testing

n/a

[github-actions]

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[github-actions]

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