Add command shell article

[sdwheeler]

PR Summary

This PR copies the command shell article from the Utility Modules docset. It includes some edits and reorganization. Once this is published, I will remove the copy from the old docset and link to this one in the TOC.

Add command shell article

• Fixes AB#372944

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.

[learn-build-service-prod]

Learn Build status updates of commit 5b2b7db:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/toc.yml	✅Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/what-is-a-command-shell.md	✅Succeeded	View (>=powershell-5.1)

For more details, please refer to the build report.

For any questions, please:

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

[learn-build-service-prod]

Learn Build status updates of commit afbad1e:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/toc.yml	✅Succeeded	View (>=powershell-5.1)
reference/docs-conceptual/what-is-a-command-shell.md	✅Succeeded	View (>=powershell-5.1)

For more details, please refer to the build report.

For any questions, please:

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