Enable setting of project_key

Allow setting of service_desk's project_key attribute (though still
behind a feature flag).

ee/app/controllers/projects/service_desk_controller.rb

@@ -22,7 +22,7 @@ class Projects::ServiceDeskController < Projects::ApplicationController
   private
 
   def setting_params
-    params.permit(:issue_template_key, :outgoing_name)
+    params.permit(:issue_template_key, :outgoing_name, :project_key)
   end
 
   def json_response
@@ -35,7 +35,8 @@ class Projects::ServiceDeskController < Projects::ApplicationController
           service_desk_enabled: project.service_desk_enabled,
           issue_template_key: service_desk_settings&.issue_template_key,
           template_file_missing: service_desk_settings&.issue_template_missing?,
-          outgoing_name: service_desk_settings&.outgoing_name
+          outgoing_name: service_desk_settings&.outgoing_name,
+          project_key: service_desk_settings&.project_key
         }
 
       format.json { render json: service_desk_attributes }

ee/app/services/service_desk_settings/update_service.rb

@@ -5,6 +5,10 @@ module ServiceDeskSettings
     def execute
       settings = ServiceDeskSetting.safe_find_or_create_by!(project_id: project.id)
 
+      unless ::Feature.enabled?(:service_desk_custom_address)
+        params.delete(:project_key)
+      end
+
       if settings.update(params)
         success
       else

ee/app/views/projects/_service_desk_settings.html.haml

@@ -14,6 +14,7 @@
           incoming_email: (@project.service_desk_address if @project.service_desk_enabled),
           selected_template: "#{@project.service_desk_setting&.issue_template_key}",
           outgoing_name: "#{@project.service_desk_setting&.outgoing_name}",
+          project_key: "#{@project.service_desk_setting&.project_key}",
           templates: issuable_templates_names(Issue.new) } }
       - elsif show_promotions? && show_callout?('promote_service_desk_dismissed')
         = render 'shared/promotions/promote_servicedesk'

ee/spec/services/service_desk_settings/update_service_spec.rb

@@ -7,13 +7,27 @@ describe ServiceDeskSettings::UpdateService do
     let_it_be(:user) { create(:user) }
 
     context 'with valid params' do
-      let(:params) { { outgoing_name: 'some name' } }
+      let(:params) { { outgoing_name: 'some name', project_key: 'foo' } }
 
       it 'updates service desk settings' do
         result = described_class.new(settings.project, user, params).execute
 
         expect(result[:status]).to eq :success
         expect(settings.reload.outgoing_name).to eq 'some name'
+        expect(settings.reload.project_key).to eq 'foo'
+      end
+
+      context 'when service_desk_custom_address is disabled' do
+        before do
+          stub_feature_flags(service_desk_custom_address: false)
+        end
+
+        it 'ignores project_key parameter' do
+          result = described_class.new(settings.project, user, params).execute
+
+          expect(result[:status]).to eq :success
+          expect(settings.reload.project_key).to be_nil
+        end
       end
     end