Change feed merge, unmerge and regeneration workers to use a replica (#25849)

app/workers/regeneration_worker.rb

@@ -6,8 +6,13 @@ class RegenerationWorker
   sidekiq_options lock: :until_executed
 
   def perform(account_id, _ = :home)
-    account = Account.find(account_id)
-    PrecomputeFeedService.new.call(account)
+    ApplicationRecord.connected_to(role: :primary) do
+      @account = Account.find(account_id)
+    end
+
+    ApplicationRecord.connected_to(role: :read, prevent_writes: true) do
+      PrecomputeFeedService.new.call(@account)
+    end
   rescue ActiveRecord::RecordNotFound
     true
   end