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/metrics/metrics.service.ts

@@ -6,6 +6,7 @@ import {
   type Meter,
   type MetricOptions,
   type ObservableGauge,
+  type ObservableResult,
 } from '@opentelemetry/api';
 import { isDefined } from 'twenty-shared/utils';
 
@@ -42,16 +43,63 @@ export class MetricsService {
     options: MetricOptions;
     callback: () => number | Promise<number>;
     cacheValue?: boolean;
+  }): ObservableGauge {
+    return this.createObservableGaugeInternal({
+      metricName,
+      options,
+      callback,
+      cacheValue,
+      observeResult: (observableResult, result) => {
+        observableResult.observe(result);
+      },
+    });
+  }
+
+  createMultiObservableGauge({
+    metricName,
+    options,
+    callback,
+    cacheValue = false,
+  }: {
+    metricName: string;
+    options: MetricOptions;
+    callback: () => Promise<Array<{ value: number; attributes: Attributes }>>;
+    cacheValue?: boolean;
+  }): ObservableGauge {
+    return this.createObservableGaugeInternal({
+      metricName,
+      options,
+      callback,
+      cacheValue,
+      observeResult: (observableResult, observations) => {
+        for (const observation of observations) {
+          observableResult.observe(observation.value, observation.attributes);
+        }
+      },
+    });
+  }
+
+  private createObservableGaugeInternal<T>({
+    metricName,
+    options,
+    callback,
+    cacheValue,
+    observeResult,
+  }: {
+    metricName: string;
+    options: MetricOptions;
+    callback: () => T | Promise<T>;
+    cacheValue: boolean;
+    observeResult: (observableResult: ObservableResult, result: T) => void;
   }): ObservableGauge {
     const gauge = this.getMeter().createObservableGauge(metricName, options);
 
     gauge.addCallback(async (observableResult) => {
       if (cacheValue) {
-        const cachedResult =
-          await this.healthCacheStorage.get<number>(metricName);
+        const cachedResult = await this.healthCacheStorage.get<T>(metricName);
 
         if (isDefined(cachedResult)) {
-          observableResult.observe(cachedResult);
+          observeResult(observableResult, cachedResult);
 
           return;
         }
@@ -60,7 +108,7 @@ export class MetricsService {
       try {
         const result = await callback();
 
-        observableResult.observe(result);
+        observeResult(observableResult, result);
 
         if (cacheValue) {
           await this.healthCacheStorage.set(