Add warning for Microsoft Defender XDR connector on offboarding

[RobbeVandenDaele]

Added a warning about reconnecting the Microsoft Defender XDR connector after offboarding. The current message is way to easily overlooked while this can have important production impact

[learn-build-service-prod]

Learn Build status updates of commit 7873e78:

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unified-secops-platform/microsoft-sentinel-onboard.md	✅Succeeded

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[prmerger-automator]

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

[prmerger-automator]

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

[ShannonLeavitt]

@batamig

Could you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding an approval and 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

[Copilot]

Pull request overview

Adds a more prominent warning in the Microsoft Sentinel offboarding instructions to highlight that offboarding from the Defender portal also disconnects the Microsoft Defender XDR connector, and that it must be reconnected to resume incident ingestion.

Changes:

• Converted the existing connector-disconnect note into a [!WARNING] admonition.
• Added explicit guidance to reconnect the Microsoft Defender XDR connector after offboarding if you want incidents to flow again.