Add code_owner_approval column to projects

The `merge_requests_require_code_owner_approval` for projects will
indicate whether or not merge requests in the project will require
approval from relevant codeowners.

db/schema.rb

@@ -2433,6 +2433,7 @@ ActiveRecord::Schema.define(version: 20190301081611) do
     t.bigint "pool_repository_id"
     t.string "runners_token_encrypted"
     t.string "bfg_object_map"
+    t.boolean "merge_requests_require_code_owner_approval"
     t.index ["ci_id"], name: "index_projects_on_ci_id", using: :btree
     t.index ["created_at"], name: "index_projects_on_created_at", using: :btree
     t.index ["creator_id"], name: "index_projects_on_creator_id", using: :btree

ee/db/migrate/20190219134239_add_merge_requests_require_codeowner_approval_to_projects.rb

+# frozen_string_literal: true
+
+class AddMergeRequestsRequireCodeownerApprovalToProjects < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    add_column :projects, :merge_requests_require_code_owner_approval, :boolean
+  end
+end