[TRI-4137] Add vanilla JS frontend support for Realtime

[matt-aitken]

We have a React hooks package (@trigger.dev/react-hooks) but no easy way of using it from other frameworks or using just JS.

Currently there's quite a lot of code inside the React hooks package, it uses our core package and has to build up state from the stream.

We should extract some of this logic out and create an export from @trigger.dev/sdk/v3/browser. With some docs, this will allow people to consume Realtime from their frontend (without React).

We aim to also have packages for other popular frameworks, this should be used by them too.

_TRI-4137