Add ResponseHeadersVariable Parameter Documentation

[markekraus]

Documents PowerShell/PowerShell#4888 wherein a new -ResponseHeadersVariable parameter was added to Invoke-RestMethod.

Version(s) of document impacted

• Impacts 6 document
• Impacts 5.1 document
• Impacts 5.0 document
• Impacts 4.0 document
• Impacts 3.0 document

Reason(s) for not updating all version of documents

• The documented feature was introduced in version 6.0.0 of PowerShell
• This issue only shows up in version (list version(s) here) of the document
• This PR partially fixes the issue, and issue # tracks the remaining work

[saldana]

✅ Validation status: passed

File	Status	Preview URL	Details
reference/6/Microsoft.PowerShell.Utility/Invoke-RestMethod.md	✅Succeeded

For more details, please refer to the build report.

Note: If you changed an existing file name or deleted a file, broken links in other files to the deleted or renamed file are listed only in the full build report.

[juanpablojofre]

Thanks Mark !! @markekraus