Update export-topics-powershell.md

[robsoto1]

I updated the article to be clearer and the user will have less reverse engineering to do.

1. Modified example script to include correct syntax
2. Add reference to missing DLL file noted in errors during failed attempts
3. Added directions for folder structure

[learn-build-service-prod]

Learn Build status updates of commit ba6a93d:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-365/topics/export-topics-powershell.md	✅Succeeded

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 dfb6d4b:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-365/topics/export-topics-powershell.md	✅Succeeded

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

[v-jmathew]

This PR has been open for an extended period of time and has conflicts. If these changes are still relevant, please re-submit them to https://github.com/MicrosoftDocs/microsoft-365-docs-pr/.