Add db migration

db/migrate/20190605104727_add_default_project_deletion_protection_to_application_settings.rb

+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddDefaultProjectDeletionProtectionToApplicationSettings < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default :application_settings, :default_project_deletion_protection, :boolean, default: false, allow_null: false
+  end
+
+  def down
+    remove_column :application_settings, :default_project_deletion_protection
+  end
+end

db/schema.rb

@@ -194,6 +194,7 @@ ActiveRecord::Schema.define(version: 20190611161641) do
     t.text "encrypted_lets_encrypt_private_key"
     t.text "encrypted_lets_encrypt_private_key_iv"
     t.boolean "dns_rebinding_protection_enabled", default: true, null: false
+    t.boolean "default_project_deletion_protection", default: false, null: false
     t.index ["usage_stats_set_by_user_id"], name: "index_application_settings_on_usage_stats_set_by_user_id", using: :btree
   end