Fix graph api error by updating the call for creating onlineMeeting. …

[iiivanov1993]

1. Fix Graph API error by updating the call for creating onlineMeeting object. Currently, "graph.microsoft.com/beta/app/onlineMeetings" with an application token is used to create an onlineMeeting object. It is deprecated as stated in the Graph API documentation: https://docs.microsoft.com/en-us/graph/api/application-post-onlinemeetings?view=graph-rest-beta&tabs=http
   "Note: The /app or /communications path with an application token is deprecated. Going forward, use the /me path with a user token to create online meetings."
   This caused the http request to fail and creation of Meeting inside of Teams returns an error.
   Fixed by using the Graph SDK:
   await GraphClient.Me.OnlineMeetings.Request().AddAsync(onlineMeeting);
2. Use IWebHostEnvironment instead of deprecated IHostingEnvironment.
3. Add exception handling pipeline returning exception messages with 500 http responses.

[msftclas]

All CLA requirements met.

[jthake]

@TBag Looks like @iiivanov1993 beat us to it from our work tonight on changing to Me.OnlineMeetings. He also has two additional adds I like.

[TBag]

Let's discuss and decide what to merge today.