Set default period in new/renew domain forms in registrar area

#495

spec/models/depp/domain_spec.rb

@@ -0,0 +1,9 @@
+require 'rails_helper'
+
+RSpec.describe Depp::Domain do
+  describe '::default_period', db: false, settings: false do
+    it 'returns default period' do
+      expect(described_class.default_period).to eq('1y')
+    end
+  end
+end