add readonly property to wp schema

config/locales/en.yml

@@ -587,6 +587,7 @@ en:
         parent_work_package: "Parent"
         priority: "Priority"
         progress: "Progress (%)"
+        readonly: "Read only"
         schedule_manually: "Manual scheduling"
         spent_hours: "Spent time"
         spent_time: "Spent time"

lib/api/v3/work_packages/schema/work_package_schema_representer.rb

@@ -176,6 +176,12 @@ module API
                  show_if: ->(*) { Setting.work_package_done_ratio != 'disabled' },
                  required: false
 
+          schema :readonly,
+                 type: 'Boolean',
+                 show_if: ->(*) { Status.can_readonly? },
+                 required: false,
+                 has_default: true
+
           schema :created_at,
                  type: 'DateTime'
 

spec/lib/api/v3/work_packages/schema/work_package_schema_representer_spec.rb

@@ -661,6 +661,25 @@ describe ::API::V3::WorkPackages::Schema::WorkPackageSchemaRepresenter do
       end
     end
 
+    describe 'readonly' do
+      context 'with the enterprise feature enabled', with_ee: %i[readonly_work_packages] do
+        it_behaves_like 'has basic schema properties' do
+          let(:path) { 'readonly' }
+          let(:type) { 'Boolean' }
+          let(:name) { I18n.t('activerecord.attributes.work_package.readonly') }
+          let(:required) { false }
+          let(:has_default) { true }
+          let(:writable) { false }
+        end
+      end
+
+      context 'without the enterprise feature' do
+        it 'has no such property' do
+          expect(subject).not_to have_json_path('readonly')
+        end
+      end
+    end
+
     describe 'createdAt' do
       it_behaves_like 'has basic schema properties' do
         let(:path) { 'createdAt' }