Requesting a VTT formatted meeting transcript show no content

[gavinbarron]

Describe the bug
We have customers encountering an issue with Graph Explorer when they download the transcript content in text/vtt format.  GE renders an empty JSON body and the customers think that the transcript is missing.  Below is the API example to download content (note the $format=text/vtt).

To Reproduce
Steps to reproduce the behavior:

1. Have an online meeting with a transcript
2. In GE request the vtt content of the transcript, e.g. https://graph.microsoft.com/v1.0/users/258e57a3-c3d6-4bce-b139-24cd9078dfcd/onlineMeetings/MSoyNThlNTdhMy1jM2Q2LTRiY2UtYjEzOS0yNGNkOTA3OGRmY2QqMCoqMTk6bWVldGluZ19Zek0yTVRJM05ETXRNell5TlMwME4yVmtMV0UyWXpBdE5qWm1PV00xWlRZM01UVXpAdGhyZWFkLnYy/transcripts/VjIjIzEyNThlNTdhMy1jM2Q2LTRiY2UtYjEzOS0yNGNkOTA3OGRmY2QyNjI0MzdmZi0zNTFkLTRmNmMtYjU0My1iYWMwOWI1YTBjMjMwNDAwMDAwMDgyMDBFMDAwNzRDNUI3MTAxQTgyRTAwODAwMDAwMDAwYTQ2YTcxMzc1Njg5ZGIwMTAwMDAwMDAwMDAwMDAwMDAxMDAwMDAwMDYzYWEzZWY4YmIyN2U0NDM5NjJlMDlkNzBlZmE3YTI5IyMzYjc1ZTQyZC01ODQ4LTRmOGUtYmM3ZS00NzcyZGZjMTRmNWE=/content?$format=text/vtt
3. The Response Pane shows an empty object

Expected behavior
A plain text rendering of the body contents provided as vtt is a plain text format. In general, if the content type of the response doesn't have a dedicated handler e.g. application/json application/xml image/jpeg etc., we should just use a plain text response rendering.

Headers from response:

Body contents:

WEBVTT

00:00:04.762 --> 00:00:07.562
<v Gavin Barron>This is a test to see how.</v>

00:00:08.302 --> 00:00:10.462
<v Gavin Barron>We can get a BTT.</v>