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/editor-ui/src/components/MainHeader/MainHeader.vue

@@ -90,11 +90,6 @@ export default defineComponent({
 	mounted() {
 		this.dirtyState = this.uiStore.stateIsDirty;
 		this.syncTabsWithRoute(this.$route);
-		// Initialize the push connection
-		this.pushConnect();
-	},
-	beforeUnmount() {
-		this.pushDisconnect();
 	},
 	watch: {
 		$route(to, from) {