Fix sidebar Iterations link logic

Change to show Iterations link when user can :read_iterations
and add :project_iterations feature flag to wrap incremental
code changes

ee/app/views/layouts/nav/sidebar/_project_iterations_link.html.haml

-- return unless License.feature_available?(:iterations)
-- return unless Feature.enabled?(:group_iterations, @group, default_enabled: true)
+- return unless Feature.enabled?(:project_iterations, @project.group, default_enabled: false)
+- return unless can?(current_user, :read_iteration, @project)
 
 = nav_link(controller: :iterations) do
   = link_to project_iterations_path(@project), title: _('Iterations') do

ee/changelogs/unreleased/222763-add-project-iteration-page.yml

----
-title: Add iteration page within projects
-merge_request: 37715
-author:
-type: added

ee/spec/features/projects/navbar_spec.rb

@@ -11,7 +11,7 @@ RSpec.describe 'Project navbar' do
   let_it_be(:project) { create(:project, :repository) }
 
   before do
-    stub_feature_flags(group_iterations: false)
+    stub_feature_flags(project_iterations: false)
 
     insert_package_nav(_('Operations'))
 
@@ -103,7 +103,7 @@ RSpec.describe 'Project navbar' do
   context 'when iterations is available' do
     before do
       stub_licensed_features(iterations: true)
-      stub_feature_flags(group_iterations: true)
+      stub_feature_flags(project_iterations: true)
 
       insert_after_sub_nav_item(
         _('Milestones'),

ee/spec/views/layouts/nav/sidebar/_project.html.haml_spec.rb

@@ -260,9 +260,9 @@ RSpec.describe 'layouts/nav/sidebar/_project' do
         stub_licensed_features(iterations: true)
       end
 
-      context 'with group iterations feature flag enabled' do
+      context 'with project_iterations feature flag enabled' do
         before do
-          stub_feature_flags(group_iterations: true)
+          stub_feature_flags(project_iterations: true)
         end
 
         it 'is visible' do
@@ -272,9 +272,9 @@ RSpec.describe 'layouts/nav/sidebar/_project' do
         end
       end
 
-      context 'with iterations feature flag disabled' do
+      context 'with project_iterations feature flag disabled' do
         before do
-          stub_feature_flags(group_iterations: false)
+          stub_feature_flags(project_iterations: false)
         end
 
         it 'is not visible' do

spec/features/projects/navbar_spec.rb

@@ -12,7 +12,7 @@ RSpec.describe 'Project navbar' do
   let_it_be(:project) { create(:project, :repository) }
 
   before do
-    stub_feature_flags(group_iterations: false)
+    stub_feature_flags(project_iterations: false)
 
     insert_package_nav(_('Operations'))