Demonstrate data streams

[ladvoc]

Summary of changes:

• Adds text stream handler for "some-topic", logs incoming messages
• Uses send text instead of publish data for sending messages

Depends on data streams support introduced in livekit/client-sdk-unity#89.

[cloudwebrtc]

The following code seems to have been removed in the last commit and forgotten to be added before room.connect?

	room.RegisterTextStreamHandler("my-topic", (data, identity) =>
                StartCoroutine(HandleTextStream(data, identity))
            );