Add "human detection" to voice OTP phone call

[zachmargolis]

Why:
So we don't read our OTPs into people's voicemails

How:
Replace intial message that reads the code with one that
prompts users to press 1 to hear the code

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Expands on #767 to add human detection

[monfresh]

I'm testing this right now, and the voice message keeps playing in a loop:

Your login.gov one time passcode is [code], again, your passcode is [code]. 
Press 1 to repeat your passcode. 
[silence for a few seconds].

This repeats seemingly ad infinitum.

Is this expected?

[zachmargolis]

@monfresh sort of expected? Unfortunately the Twimlet code for menus includes a <Redirect> tag after the menu which will cause the whole script to loop after a timeout (see example menu xml)

We'll have to sort out the infinite looping with #761 when we can self-host the TwiML and have more control over menu behavior.

Based on some discussion with @usdsclarax in https://github.com/18F/identity-private/issues/604, I'm going to close this issue since our current thinking is we don't need/want human detection.