OUTPUTS seems to be String not PSPipeline (#17287)

When I execute `Invoke-AzDataFactoryV2Pipeline`, String was returned. So, OUTPUTS seems to be System.String not Microsoft.Azure.Commands.DataFactoryV2.Models.PSPipeline.

Author: ecormaksin

src/DataFactory/DataFactoryV2/help/Invoke-AzDataFactoryV2Pipeline.md

@@ -277,7 +277,7 @@ This cmdlet supports the common parameters: -Debug, -ErrorAction, -ErrorVariable
 
 ## OUTPUTS
 
-### Microsoft.Azure.Commands.DataFactoryV2.Models.PSPipeline
+### System.String
 
 ## NOTES