Support for Broadcast

[victorsa72]

Support for Broadcast

Requesting support for Broadcast functionality, as described here: https://supabase.com/docs/guides/realtime/extensions/broadcast

I believe the solution would be to add a new ChannelEvent enum (.broadcast) with all the associated fix ups for init(), isLifeCycleEvent() and rawValue.

Additional reference from https://supabase.com/docs/guides/realtime/protocol:

{
   "event": "broadcast",
   "topic": string,
   "payload": {
      "event": string,
      "payload": {[key: string]: boolean | number | string | null | undefined},
      "type": "broadcast"
   },
   "ref": null
}

[foodisbeast]

If still in need try update-upstream branch (see #26)