Add requirements index action

This action will be used by FE to setup Vue objects for
Requirements UI.

ee/app/controllers/projects/requirements_controller.rb

+# frozen_string_literal: true
+
+class Projects::RequirementsController < Projects::ApplicationController
+  before_action :authorize_read_requirement!
+  before_action :verify_requirements_management_flag!
+  before_action do
+    push_frontend_feature_flag(:requirements_management, project)
+  end
+
+  def index
+    respond_to do |format|
+      format.html
+    end
+  end
+
+  private
+
+  def verify_requirements_management_flag!
+    render_404 unless Feature.enabled?(:requirements_management, project)
+  end
+end

ee/app/views/projects/requirements/index.html.haml

+= _('Not Implemented')

ee/config/routes/project.rb

@@ -11,6 +11,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
       # Begin of the /-/ scope.
       # Use this scope for all new project routes.
       scope '-' do
+        resources :requirements, only: [:index]
         resources :packages, only: [:index, :show, :destroy], module: :packages
         resources :package_files, only: [], module: :packages do
           member do

ee/spec/controllers/projects/requirements_controller_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Projects::RequirementsController do
+  let_it_be(:project) { create(:project) }
+  let_it_be(:user) { create(:user) }
+
+  subject { get :index, params: { namespace_id: project.namespace, project_id: project } }
+
+  describe 'GET #index' do
+    context 'with authorized user' do
+      before do
+        project.add_developer(user)
+        sign_in(user)
+      end
+
+      context 'when feature is available' do
+        before do
+          stub_licensed_features(requirements: true)
+        end
+
+        it 'renders the index template' do
+          subject
+
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(response).to render_template(:index)
+        end
+
+        context 'when requirements_management flag is disabled' do
+          before do
+            stub_feature_flags(requirements_management: false)
+          end
+
+          it 'returns 404' do
+            subject
+
+            expect(response).to have_gitlab_http_status(:not_found)
+          end
+        end
+      end
+
+      context 'when feature is not available' do
+        before do
+          stub_licensed_features(requirements: false)
+        end
+
+        it 'returns 404' do
+          subject
+
+          expect(response).to have_gitlab_http_status(:not_found)
+        end
+      end
+    end
+
+    context 'with unauthorized user' do
+      before do
+        sign_in(user)
+      end
+
+      context 'when feature is available' do
+        before do
+          stub_licensed_features(requirements: true)
+        end
+
+        it 'returns 404' do
+          subject
+
+          expect(response).to have_gitlab_http_status(:not_found)
+        end
+      end
+    end
+
+    context 'with anonymous user' do
+      it 'returns 302' do
+        subject
+
+        expect(response).to have_gitlab_http_status(:found)
+        expect(response).to redirect_to(new_user_session_path)
+      end
+    end
+  end
+end