[Response Ops][Alerting] Grouping ad hoc run metrics under alerting metrics (#233875)

Towards elastic/response-ops-team#297

## Summary

Updates the grouping for task manager per task type metrics to
categorize `ad_hoc_run-backfill` task types under the `alerting`
grouping.

## To Verify

1. Start ES and Kibana
2. Create a detection rule
3. Manually schedule a backfill for the detection rule
4. Navigate to the task manager metrics
endpoint(https://localhost:5601/api/task_manager/metrics?reset=false)
and verify that the success counter for `alerting` (under
`metrics.task_run.value.by_type.alerting`) is incremented, as well as
the success counter for `ad_hoc_run-backfill` (under
`metrics.task_run.value.by_type.ad_hoc_run-backfill`). (The counters
reset every 30 seconds so you will have to look at this endpoint quickly
after scheduling the backfill).

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

Author: ymao1

x-pack/platform/plugins/shared/task_manager/server/metrics/lib/get_task_type_group.test.ts

@@ -13,6 +13,10 @@ describe('getTaskTypeGroup', () => {
     expect(getTaskTypeGroup('actions:def')).toEqual('actions');
   });
 
+  test('should correctly group ad hoc runs under alerting', () => {
+    expect(getTaskTypeGroup('ad_hoc_run-backfill')).toEqual('alerting');
+  });
+
   test('should return undefined if no match', () => {
     expect(getTaskTypeGroup('alerting-abc')).toBeUndefined();
     expect(getTaskTypeGroup('fooalertingbar')).toBeUndefined();

x-pack/platform/plugins/shared/task_manager/server/metrics/lib/get_task_type_group.ts

@@ -5,9 +5,16 @@
  * 2.0.
  */
 
-const taskTypeGrouping = new Set<string>(['alerting:', 'actions:']);
+const ALERT_GROUP = 'alerting';
+const ACTIONS_GROUP = 'actions';
+const taskTypeGrouping = new Set<string>([`${ALERT_GROUP}:`, `${ACTIONS_GROUP}:`]);
 
 export function getTaskTypeGroup(taskType: string): string | undefined {
+  // we want to group ad hoc runs under alerting
+  if (taskType === 'ad_hoc_run-backfill') {
+    return ALERT_GROUP;
+  }
+
   for (const group of taskTypeGrouping) {
     if (taskType.startsWith(group)) {
       return group.replace(':', '');