fix: add queue attribute to jobs waiting gauge metric (#21324)

## Summary
- The `twenty_queue_jobs_waiting_total` gauge was summing all queues
into a single value without a `queue` label, making the Grafana "Jobs
Waiting by Queue" panel show a single aggregated line instead of
per-queue breakdown.
- Uses `getMeter()` directly to call `observableResult.observe(count, {
queue: queueName })` per queue, matching the `by (queue)` grouping the
dashboard already expects.

## Test plan
- [x] Deploy and verify the Grafana "Jobs Waiting by Queue" panel
displays separate series per queue
- [x] Confirm Prometheus scrape returns
`twenty_queue_jobs_waiting_total{queue="..."}` with distinct queue
labels

packages/twenty-server/src/engine/core-modules/message-queue/drivers/bullmq.driver.ts

@@ -54,17 +54,23 @@ export class BullMQDriver
   ) {}
 
   onModuleInit() {
-    this.metricsService.createObservableGauge({
+    this.metricsService.createMultiObservableGauge({
       metricName: 'twenty_queue_jobs_waiting_total',
       options: { description: 'Current number of jobs waiting in queue' },
       callback: async () => {
-        let totalWaiting = 0;
+        const observations: Array<{
+          value: number;
+          attributes: { queue: string };
+        }> = [];
 
         for (const [queueName, queue] of Object.entries(this.queueMap)) {
           try {
             const waitingCount = await queue.count();
 
-            totalWaiting += waitingCount;
+            observations.push({
+              value: waitingCount,
+              attributes: { queue: queueName },
+            });
           } catch (error) {
             this.logger.error(
               `Failed to collect waiting jobs metrics for queue ${queueName}`,
@@ -73,7 +79,7 @@ export class BullMQDriver
           }
         }
 
-        return totalWaiting;
+        return observations;
       },
     });
   }