Update dnssec-how-to.md adding App service domain DNSSEC limitation

[RutujaJadhav1710]

Coming form Azure networking Support engineer [email protected].

I had a case where customer was unable to enable DNSSEC on the domain he created via App Service. App Service Domain PG is currently working on it, but there is no ETA. This information has been confirmed with [email protected].

[prmerger-automator]

@RutujaJadhav1710 : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit ec3d9e8:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/dns/dnssec-how-to.md	✅Succeeded

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[Copilot]

Pull Request Overview

This PR adds documentation about a DNSSEC limitation for App Service Domain to the Azure DNS DNSSEC how-to guide. The update informs users that domains registered through App Service Domain cannot enable DNSSEC functionality.

Key changes:

• Added an important notice about App Service Domain DNSSEC limitation

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[ShannonLeavitt]

@asudbring

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[asudbring]

#sign-off