Add index services on template

This migration is a corrective action to add the missing
index_services_on_template index on staging.

We suspect the column rename was executed in staging already before it
was rolled back/reverted with 8d4d9705. The rollback doesn't know about
the existence of the index though and hence it is now missing.

db/migrate/20200309105539_add_index_services_on_template.rb

+# frozen_string_literal: true
+
+class AddIndexServicesOnTemplate < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  # This migration is a corrective action to add the missing
+  # index_services_on_template index on staging.
+  def up
+    add_concurrent_index(:services, :template) unless index_exists?(:services, :template)
+  end
+
+  def down
+    # No reverse action as this is a corrective migration.
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2020_03_06_170531) do
+ActiveRecord::Schema.define(version: 2020_03_09_105539) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"