Add note that the procedure requires tenant Entra ID P2

[JustinGrote]

Clarify that this procedure requires Microsoft Entra ID P2.

That's important to MSSPs, if they want to onboard a customer using this, their customer has to pay for ID P2 according to the licensing sheet, it does not say that the MSSP's licensing can be reused. That is an expensive proposition and one most customers won't go for.

[learn-build-service-prod]

Learn Build status updates of commit f38095b:

⚠️ Validation status: warnings

File	Status	Preview URL	Details
defender-xdr/mssp-access.md	⚠️Warning		Details

defender-xdr/mssp-access.md

• Line 30, Column 88: [Warning: hard-coded-locale - See documentation] Link 'https://learn.microsoft.com/en-us/entra/id-governance/licensing-fundamentals#how-can-i-license-usage-of-microsoft-entra-id-governance-features-for-business-guests' contains locale code 'en-us'. For localizability, remove 'en-us' from links to most Microsoft sites.
• Line 30, Column 88: [Suggestion: docs-link-absolute - See documentation] Absolute link 'https://learn.microsoft.com/en-us/entra/id-governance/licensing-fundamentals#how-can-i-license-usage-of-microsoft-entra-id-governance-features-for-business-guests' will be broken in isolated environments. Replace with a relative link.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel