Add the ability to send DataMessages to the Meeting while in SignallingOnly mode

[Ardenexal]

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Tell us about your request

What do you want us to build?

Which Amazon Chime SDK or feature area is this request for? amazon-chime-sdk-js

Tell us about the problem you are trying to solve and why is it hard?

We use the Chime SDK for telehealth sessions. Currently, we are trying to implement a way to Admit a patient into a telehealth session. From the documentation, it looked as though we could use AudioVideo.start({signallingOnly: true}) And then send a request to the practitioner who would then admit the patient into the session.

The Proposed User workflow would work something like this

1. Practitioner joins the session
2. Patient is now allowed to join the session
3. Patient clicks on the join button and is greeted with a Waiting for the practitioner to accept invitation message. This will run `AudioVideo.start({signallingOnly:true}) to start the communication with the room
4. using the DataChannel the object is sent to the practitioner where the practitioner received it and is then given an option to admit the patient
5. Once the patient has been accepted we then call AudioVideo.start() to enter the meeting

How are you currently solving a problem?

We are exploring multiple solutions including setting up our own WebSocket to enable this functionality. Or potentially using the AWS Chime Messaging API.

Another option we've tried is to start the session but mute the output audio and the camera/microphone but there is a lot of scenarios to watch out for like making sure we still subscribe to the AddendeePresenseId promise so that when they are admitted they can see the statuses of the other users.

Additional context

Anything else we should know?

[ReflexFox]

I need that too!