santad: Bump QoS of notify handling queue (#1342)

The use of the background queue is a historical artifact from when Santa had its own kernel extension with separate in-kernel queues for processing AUTH & NOTIFY type events. With the move to ES and the larger number of event types that we now notify on, running at the background QoS carries a small risk that the thread processing these events is not given a chance to run often enough that the queue grows and increases memory usage.

Source/santad/EventProviders/SNTEndpointSecurityClient.mm

@@ -89,10 +89,8 @@ - (instancetype)initWithESAPI:(std::shared_ptr<EndpointSecurityAPI>)esApi
       dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_CONCURRENT_WITH_AUTORELEASE_POOL,
                                               QOS_CLASS_USER_INTERACTIVE, 0));
 
-    _notifyQueue = dispatch_queue_create(
-      "com.google.santa.daemon.notify_queue",
-      dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_CONCURRENT_WITH_AUTORELEASE_POOL,
-                                              QOS_CLASS_BACKGROUND, 0));
+    _notifyQueue = dispatch_queue_create("com.google.santa.daemon.notify_queue",
+                                         DISPATCH_QUEUE_CONCURRENT_WITH_AUTORELEASE_POOL);
   }
   return self;
 }