add attachment cache worker to a prioritary queue

app/workers/attachment_cache_worker.rb

 class AttachmentCacheWorker
   require 'fileutils'
-
   include Sidekiq::Worker
 
+  sidekiq_options queue: :attachment_cache
+
   def perform(id, directory, force = false)
     @attachment = LearningObject::Attachment.find(id)
     client = DspaceService.create_client

config/sidekiq.yml

@@ -11,7 +11,9 @@
   - default
   - score
   - convert_video
-  - [high_priority, 2]
+  - searchkick
+  - [attachment_cache, 2]
+  - [high_priority, 5]
 # :daemon: true
 
 development: &development