Support Amazon Polly for TTS

In Home Assistant I’ve used Amazon Polly in the past for TTS. Since Google WaveNet is supported, perhaps we can support Amazon Polly as well directly in Rhasspy?

Otherwise I have to use probably the conversation integration to get the intent across and use an intent script to react to it and send a TTS message.

The disadvantage of this approach is that the location playing the TTS message will not be the Rhasspy satellite in case it doesn’t run also Home Assistant, like in my current setup.