Fix New-Item in Provider cmdlets documentation

[aberus]

PR Summary

Updated the cmdlet incorrect name of cmdlet for creating new item from New-ItemProperty to New-Item and clarified its purpose.

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 contributor's guide.
• Style: This PR adheres to the style guide.

[learn-build-service-prod]

PoliCheck Scan Report

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[learn-build-service-prod]

Learn Build status updates of commit 3e3bf09:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/developer/provider/provider-cmdlets.md	✅Succeeded	View (>=powershell-5.1)

For more details, please refer to the build report.

[sdwheeler]

@aberus Thanks for the fix