[Feature Request] Add support for ws.send_event to a clientside EventBus

The persistent ws callbacks really are great! But I'm missing one feature, the ability to send data directly to clientside JS code.

Is your feature request related to a problem? Please describe. I have persistent ws-callbacks that sends updates with ws.set_props. Some of the updates needs to run plain JS code (I'm modifies a SVG in realtime based on ws updates)

Describe the solution you'd like It would be great if the websocket update also could write to an eventbus that js-code can hook on to and listen to.

Describe alternatives you've considered I've been exploring sending updates via a dcc.Storage and have a clientside callback that act on changes on the dcc.Storage but, this have limitations in rates, if I send updates (with ws.set_props) too frequently some messages are lost, the clientside callback never gets fired. Now we have a asyncio.sleep(0.1) to allow some time for the clientside to pick up the changes. The best solution here would be a channel directly to the JS-code.