Adjust NullifyOrphanRunnerIdOnCiBuilds batch parameters

In GitLabCom, 100k batch size and 1k sub batch size took more than
2 minutes. So, we decided to start lower than those parameters.

Also, we will allow the batch size to increase up 150k if it's possible

Changelog: other

db/post_migrate/20220223112304_schedule_nullify_orphan_runner_id_on_ci_builds.rb

@@ -3,9 +3,9 @@
 class ScheduleNullifyOrphanRunnerIdOnCiBuilds < Gitlab::Database::Migration[1.0]
   MIGRATION = 'NullifyOrphanRunnerIdOnCiBuilds'
   INTERVAL = 2.minutes
-  BATCH_SIZE = 100_000
-  MAX_BATCH_SIZE = 100_000 # 100k * 25k = 2.5B ci_builds
-  SUB_BATCH_SIZE = 1_000
+  BATCH_SIZE = 50_000
+  MAX_BATCH_SIZE = 150_000
+  SUB_BATCH_SIZE = 500
 
   def up
     queue_batched_background_migration(