Schedule async weekend build of index for job traces

Changelog: performance

db/post_migrate/20220224000000_async_build_trace_expire_at_index.rb

+# frozen_string_literal: true
+
+class AsyncBuildTraceExpireAtIndex < Gitlab::Database::Migration[1.0]
+  INDEX_NAME = 'tmp_index_ci_job_artifacts_on_id_where_trace_and_expire_at'
+  TIMESTAMPS = "'2021-04-22 00:00:00', '2021-05-22 00:00:00', '2021-06-22 00:00:00', '2022-01-22 00:00:00', '2022-02-22 00:00:00', '2022-03-22 00:00:00', '2022-04-22 00:00:00'"
+
+  def up
+    prepare_async_index :ci_job_artifacts, :id, where: "file_type = 3 AND expire_at IN (#{TIMESTAMPS})", name: INDEX_NAME
+  end
+
+  def down
+    unprepare_async_index :ci_builds, :id, name: INDEX_NAME
+  end
+end

db/schema_migrations/20220224000000

+74b4d572118b7f5da0a80722601a4757ce47ccbdae1af1e84b2304343477d634
\ No newline at end of file

ee/spec/migrations/async_build_trace_expire_at_index_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20220224000000_async_build_trace_expire_at_index.rb')
+
+RSpec.describe AsyncBuildTraceExpireAtIndex do
+  describe '#up' do
+    it 'sets up a delayed concurrent index creation' do
+      expect_next_instance_of(described_class) do |instance|
+        expect(instance).to receive(:prepare_async_index)
+      end
+
+      migrate!
+    end
+  end
+
+  describe '#down' do
+    it 'removes an index' do
+      expect_any_instance_of(described_class) do |instance|
+        expect(instance).to receive(:unprepare_async_index)
+      end
+
+      schema_migrate_down!
+    end
+  end
+end