Update Install-ADServiceAccount.md

[HerbertMauerer]

Clarification on the use of the cmdlet.

PR Checklist

• [ ] Descriptive Title: Clarifies the use of the cmdlet for MSA vs. GMSA.
• [ ] Summary: The cmdlet is only providing value for MSAs.
• [ ] Contributor's Guide: I have read the contributors guide.
• [ ] Style: This PR adheres to the style guide.

[learn-build-service-prod[bot]]

Learn Build status updates of commit 560a9c5:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
docset/winserver2022-ps/activedirectory/Install-ADServiceAccount.md	:white_check_mark:Succeeded	View (WindowsServer2022-ps)

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