Creates asynchronously index on ci_job_artifacts table

The index will be used to fix job artifacts size for gitlab
instances which is currently broken. This will be fixed in a
separated MR.

Changelog: added

db/post_migrate/20220310095341_add_async_index_ci_job_artifacts_project_id_created_at.rb

+# frozen_string_literal: true
+
+# See https://docs.gitlab.com/ee/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddAsyncIndexCiJobArtifactsProjectIdCreatedAt < Gitlab::Database::Migration[1.0]
+  INDEX_NAME = 'index_ci_job_artifacts_on_id_project_id_and_created_at'
+
+  def up
+    prepare_async_index :ci_job_artifacts, [:project_id, :created_at, :id], name: INDEX_NAME
+  end
+
+  def down
+    unprepare_async_index_by_name :ci_job_artifacts, INDEX_NAME
+  end
+end

db/schema_migrations/20220310095341

+56d906eac31954988bd0659eabbc9f1bad1a47dd616fb99e4b90b56b2bf4c6a0
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