Run pages background migration slower

We're afraid of performance impact on self-managed instances

db/post_migrate/20210302150310_schedule_migrate_pages_to_zip_storage.rb

@@ -6,8 +6,8 @@ class ScheduleMigratePagesToZipStorage < ActiveRecord::Migration[6.0]
   DOWNTIME = false
 
   MIGRATION = 'MigratePagesToZipStorage'
-  BATCH_SIZE = 100
-  BATCH_TIME = 6.minutes
+  BATCH_SIZE = 10
+  BATCH_TIME = 5.minutes
 
   disable_ddl_transaction!
 

spec/migrations/schedule_migrate_pages_to_zip_storage_spec.rb

@@ -38,7 +38,7 @@ RSpec.describe ScheduleMigratePagesToZipStorage, :sidekiq_might_not_need_inline,
 
         migrate!
 
-        expect(migration_name).to be_scheduled_delayed_migration(6.minutes, first_id, last_id)
+        expect(migration_name).to be_scheduled_delayed_migration(5.minutes, first_id, last_id)
         expect(BackgroundMigrationWorker.jobs.size).to eq(1)
       end
     end