Add missing -ProtectPrivateKey parameter to Import-PfxCertificate documentation

[Synertry]

PR Summary

Add missing -ProtectPrivateKey parameter to the Import-PfxCertificate cmdlet documentation.
Parameter functionality is synonymous with the import option "Protect private key using virtualized-based security(Non-exportable)" in the Certificate Import Wizard:

Functionality of the option is explained by Crypt32 (Vadims Podans), creator of PSPKI:
https://security.stackexchange.com/a/186523/268642

Explanation for enum option vsm is hinted in the documentation for Virtualization-based Security (VBS).

Virtual Secure Mode (VSM) capabilities were introduced in Windows 10 and Windows Server 2016, that is why the update only ranges until there.

• Resolves what does the '-ProtectPrivateKey' switch do? #3263

PR Checklist

• Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• Summary: This PR's summary describes the scope and intent of the change.
• Contributor's Guide: I have read the contributors guide.
• Style: This PR adheres to the style guide.

[Synertry]

@microsoft-github-policy-service agree

[learn-build-service-prod]

Learn Build status updates of commit e06c290:

✅ Validation status: passed

File	Status	Preview URL	Details
docset/winserver2016-ps/pki/Import-PfxCertificate.md	✅Succeeded	View (WindowsServer2016-ps)
docset/winserver2019-ps/pki/Import-PfxCertificate.md	✅Succeeded	View (WindowsServer2019-ps)
docset/winserver2022-ps/pki/Import-PfxCertificate.md	✅Succeeded	View (WindowsServer2022-ps)
docset/winserver2025-ps/pki/Import-PfxCertificate.md	✅Succeeded	View (WindowsServer2025-ps)

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