Add worker_poll_complete_on_shutdown namespace capability

This capability indicates whether the server supports server-side
completion of outstanding worker polls on shutdown. When enabled,
the server will complete polls for workers that send WorkerInstanceKey
in their poll requests and call ShutdownWorker with the same key.

Author: rkannan82

temporal/api/namespace/v1/message.proto

@@ -42,6 +42,12 @@ message NamespaceInfo {
         bool workflow_pause = 6;
         // True if the namespace supports standalone activities
         bool standalone_activities = 7;
+        // True if the namespace supports server-side completion of outstanding worker polls on shutdown.
+        // When enabled, the server will complete polls for workers that send WorkerInstanceKey in their
+        // poll requests and call ShutdownWorker with the same WorkerInstanceKey. The poll will return
+        // an empty response. When this flag is true, workers should allow polls to return gracefully
+        // rather than terminating any open polls on shutdown.
+        bool worker_poll_complete_on_shutdown = 8;
     }
 
     // Namespace configured limits