Add Trial Experiment menu to group sidebar

In this commit we refactor the Trial Experiment menu to the new
group sidebar refactor. This menu is quite special as it doesn't
follow the same UI structure as the other menus.

Because of that, we're introducing a new behavior to allow
menu render specic partials.

app/views/layouts/nav/sidebar/_group_menus.html.haml

 - issues_count = cached_issuables_count(@group, type: :issues)
 - merge_requests_count = cached_issuables_count(@group, type: :merge_requests)
 
-= render_if_exists 'layouts/nav/sidebar/group_trial_status_widget', group: @group
-
 - if group_sidebar_link?(:overview)
   - paths = group_overview_nav_link_paths
   = nav_link(path: paths, unless: -> { current_path?('groups/contribution_analytics#show') }, html_options: { class: 'home' }) do

app/views/shared/nav/_sidebar_menu.html.haml

 = nav_link(**sidebar_menu.all_active_routes, html_options: sidebar_menu.nav_link_html_options) do
+  - if sidebar_menu.menu_with_partial?
+    = render_if_exists sidebar_menu.menu_partial, **sidebar_menu.menu_partial_options
+  - else
     = link_to sidebar_menu.link, **sidebar_menu.container_html_options, data: { qa_selector: 'sidebar_menu_link', qa_menu_item: sidebar_menu.title } do
       - if sidebar_menu.icon_or_image?
         %span.nav-icon-container

ee/lib/ee/sidebars/groups/panel.rb

+# frozen_string_literal: true
+
+module EE
+  module Sidebars
+    module Groups
+      module Panel
+        extend ::Gitlab::Utils::Override
+
+        override :configure_menus
+        def configure_menus
+          super
+
+          add_menu(::Sidebars::Groups::Menus::TrialExperimentMenu.new(context))
+        end
+      end
+    end
+  end
+end

ee/lib/sidebars/groups/menus/trial_experiment_menu.rb

+# frozen_string_literal: true
+
+module Sidebars
+  module Groups
+    module Menus
+      class TrialExperimentMenu < ::Sidebars::Menu
+        override :menu_partial
+        def menu_partial
+          'layouts/nav/sidebar/group_trial_status_widget'
+        end
+
+        override :menu_partial_options
+        def menu_partial_options
+          {
+            group: context.group
+          }
+        end
+      end
+    end
+  end
+end

lib/sidebars/concerns/has_partial.rb

+# frozen_string_literal: true
+
+# This module has the necessary methods to render
+# menus using a custom partial
+module Sidebars
+  module Concerns
+    module HasPartial
+      def menu_partial
+        nil
+      end
+
+      def menu_partial_options
+        {}
+      end
+
+      def menu_with_partial?
+        menu_partial.present?
+      end
+    end
+  end
+end

lib/sidebars/groups/panel.rb

@@ -20,3 +20,5 @@ module Sidebars
     end
   end
 end
+
+Sidebars::Groups::Panel.prepend_mod_with('Sidebars::Groups::Panel')

lib/sidebars/menu.rb

@@ -12,6 +12,7 @@ module Sidebars
     include ::Sidebars::Concerns::Renderable
     include ::Sidebars::Concerns::ContainerWithHtmlOptions
     include ::Sidebars::Concerns::HasActiveRoutes
+    include ::Sidebars::Concerns::HasPartial
 
     attr_reader :context
     delegate :current_user, :container, to: :@context
@@ -29,7 +30,7 @@ module Sidebars
 
     override :render?
     def render?
-      has_renderable_items?
+      has_renderable_items? || menu_with_partial?
     end
 
     # Menus might have or not a link

spec/lib/sidebars/menu_spec.rb

@@ -26,6 +26,14 @@ RSpec.describe Sidebars::Menu do
       it 'returns false' do
         expect(menu.render?).to be false
       end
+
+      context 'when menu has a partial' do
+        it 'returns true' do
+          allow(menu).to receive(:menu_partial).and_return('foo')
+
+          expect(menu.render?).to be true
+        end
+      end
     end
 
     context 'when the menu has items' do