Investigate how web based IDM Clients could discover wallets running on various domains

## Description

In the IDM Concept paper, we mention this:

> There will be a reference IDM Bridge written in JavaScript that will solve scenario `1` by leveraging the [postMessage API](https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage) to create a communication channel between IDM Clients and a IDM Wallet running on a pre-defined domain

Ideally, we would query which wallets are available instead of assuming the one from a pre-defined domain. To do this, we would need to broadcast a postMessage and listen for responses, but unfortunately there's no way to do that with the postMessage API.

One possible solution might be with WebRTC.

## Acceptance Criteria

- [ ] Investigate if it's possible to use WebRTC or similar technologies to discover wallets running on arbitrary domains
- [ ] If there is, update the IDM Concept paper

Start with the IDM Concept paper's discussion of the JavaScript IDM Bridge and its use of the postMessage API, then investigate whether WebRTC or similar browser technologies can discover wallets on arbitrary domains. Done means documenting whether discovery is feasible and updating the IDM Concept paper if it is.

Written by the indexing model from the issue text.