Set feature_category for service desk worker

This worker is used specifically by service desk, so we should set
service_desk category for it.

app/workers/all_queues.yml

@@ -2777,7 +2777,7 @@
   :tags: []
 - :name: service_desk_email_receiver
   :worker_name: ServiceDeskEmailReceiverWorker
-  :feature_category: :issue_tracking
+  :feature_category: :service_desk
   :has_external_dependencies:
   :urgency: :low
   :resource_boundary: :unknown

app/workers/service_desk_email_receiver_worker.rb

@@ -3,6 +3,7 @@
 class ServiceDeskEmailReceiverWorker < EmailReceiverWorker # rubocop:disable Scalability/IdempotentWorker
   include ApplicationWorker
 
+  feature_category :service_desk
   sidekiq_options retry: 3
 
   def should_perform?