feat(editor): Show avatars for users currently working on the same workflow (#7763)

This PR introduces the following changes:
- New Vue stores: `collaborationStore` and `pushConnectionStore`
- Front-end push connection handling overhaul: Keep only a singe
connection open and handle it from the new store
- Add user avatars in the editor header when there are multiple users
working on the same workflow
- Sending a heartbeat event to back-end service periodically to confirm
user is still active

- Back-end overhauls (authored by @tomi):
  - Implementing a cleanup procedure that removes inactive users
  - Refactoring collaboration service current implementation

---------

Co-authored-by: Tomi Turtiainen <10324676+tomi@users.noreply.github.com>

packages/cli/src/push/index.ts

@@ -30,6 +30,14 @@ export class Push extends EventEmitter {
 
 	private backend = useWebSockets ? Container.get(WebSocketPush) : Container.get(SSEPush);
 
+	constructor() {
+		super();
+
+		if (useWebSockets) {
+			this.backend.on('message', (msg) => this.emit('message', msg));
+		}
+	}
+
 	handleRequest(req: SSEPushRequest | WebSocketPushRequest, res: PushResponse) {
 		const {
 			userId,
@@ -37,7 +45,6 @@ export class Push extends EventEmitter {
 		} = req;
 		if (req.ws) {
 			(this.backend as WebSocketPush).add(sessionId, userId, req.ws);
-			this.backend.on('message', (msg) => this.emit('message', msg));
 		} else if (!useWebSockets) {
 			(this.backend as SSEPush).add(sessionId, userId, { req, res });
 		} else {