[Prometheus]: Mark ALERTS synthetic metric as a gauge (#99328)

Mark ALERTS synthetic metric as a gauge

It's not a counter. It can go down in value, but counters cannot

packages/grafana-prometheus/src/language_utils.test.ts

@@ -91,7 +91,7 @@ describe('parseSelector()', () => {
 describe('fixSummariesMetadata', () => {
   const synthetics = {
     ALERTS: {
-      type: 'counter',
+      type: 'gauge',
       help: 'Time series showing pending and firing alerts. The sample value is set to 1 as long as the alert is in the indicated active (pending or firing) state.',
     },
   };

packages/grafana-prometheus/src/language_utils.ts

@@ -323,7 +323,7 @@ export function fixSummariesMetadata(metadata: { [metric: string]: PromMetricsMe
   // Synthetic series
   const syntheticMetadata: PromMetricsMetadata = {};
   syntheticMetadata['ALERTS'] = {
-    type: 'counter',
+    type: 'gauge',
     help: 'Time series showing pending and firing alerts. The sample value is set to 1 as long as the alert is in the indicated active (pending or firing) state.',
   };