add dead jobs size to sidekiq api metrics

changelogs/unreleased/add-dead-jobs-to-api-sidekiq-metrics.yml

+---
+title: Add dead jobs to Sidekiq metrics API
+merge_request: 19350
+author: Marco Peterseil
+type: added

doc/api/sidekiq_metrics.md

@@ -92,7 +92,8 @@ Example response:
   "jobs": {
     "processed": 2,
     "failed": 0,
-    "enqueued": 0
+    "enqueued": 0,
+    "dead": 0
   }
 }
 ```
@@ -145,7 +146,8 @@ Example response:
   "jobs": {
     "processed": 2,
     "failed": 0,
-    "enqueued": 0
+    "enqueued": 0,
+    "dead": 0
   }
 }
 ```

lib/api/sidekiq_metrics.rb

@@ -36,7 +36,8 @@ module API
         {
           processed: stats.processed,
           failed: stats.failed,
-          enqueued: stats.enqueued
+          enqueued: stats.enqueued,
+          dead: stats.dead_size
         }
       end
     end