[formrecognizer] show all available fields in invoice sample

[kristapratico]

This sample form should return all 26 fields: https://docs.microsoft.com/en-us/azure/cognitive-services/form-recognizer/media/sample-invoice.jpg

We should update our sync / async invoice samples to use this sample form and print all available fields.

Supported fields by name can be found on this page: https://westcentralus.dev.cognitive.microsoft.com/docs/services/form-recognizer-api-v2-1-preview-2/operations/5ed8c9acb78c40a2533aee83