Add support for on-prem microsoft tts

[davehorton]

Currently this mod_azure_transcribe only works with the hosted Microsoft speech endpoint; i.e. we connect like this

SpeechConfig::FromSubscription(subscriptionKey, region);

or, if we are connecting to a hosted custom speech model, like this:

SpeechConfig::FromEndpoint(endpoint, subscriptionKey) :     

In either case, we are connecting to service that Azure is hosting. However, Azure also supports on-prem deployments. In that case, we would use:

SpeechConfig::FromHost(host)

Please see this link for details.

[xquanluu]

close as PR mereged