Conditionally render create group buttons

- This is added to the old and new top nav

Changelog: fixed

app/helpers/nav/top_nav_helper.rb

@@ -276,7 +276,11 @@ module Nav
       builder = ::Gitlab::Nav::TopNavMenuBuilder.new
       builder.add_primary_menu_item(id: 'your', title: _('Your groups'), href: dashboard_groups_path)
       builder.add_primary_menu_item(id: 'explore', title: _('Explore groups'), href: explore_groups_path)
+
+      if current_user.can_create_group?
         builder.add_secondary_menu_item(id: 'create', title: _('Create group'), href: new_group_path)
+      end
+
       builder.build
     end
   end

app/views/layouts/nav/groups_dropdown/_show.html.haml

@@ -12,6 +12,7 @@
       = nav_link(path: 'groups#explore') do
         = link_to explore_groups_path, data: { track_label: "groups_dropdown_explore_groups", track_event: "click_link" } do
           = _('Explore groups')
+      - if current_user.can_create_group?
         = nav_link(path: 'groups/new#create-group-pane', html_options: { class: 'gl-border-0 gl-border-t-1 gl-border-solid gl-border-gray-100' }) do
           = link_to new_group_path(anchor: 'create-group-pane'), data: { track_label: "groups_dropdown_create_group", track_event: "click_link" } do
             = _('Create group')

spec/helpers/nav/top_nav_helper_spec.rb

@@ -7,6 +7,7 @@ RSpec.describe Nav::TopNavHelper do
 
   let_it_be(:user) { build_stubbed(:user) }
   let_it_be(:admin) { build_stubbed(:user, :admin) }
+  let_it_be(:external_user) { build_stubbed(:user, :external, can_create_group: false) }
 
   let(:current_user) { nil }
 
@@ -305,6 +306,14 @@ RSpec.describe Nav::TopNavHelper do
             expect(groups_view[:linksSecondary]).to eq(expected_links_secondary)
           end
 
+          context 'with external user' do
+            let(:current_user) { external_user }
+
+            it 'does not have create group link' do
+              expect(groups_view[:linksSecondary]).to eq([])
+            end
+          end
+
           context 'with current nav as group' do
             before do
               helper.nav('group')