Introduce policy check for clusters navigation option

app/helpers/projects_helper.rb

@@ -293,6 +293,7 @@ module ProjectsHelper
       snippets:         :read_project_snippet,
       settings:         :admin_project,
       builds:           :read_build,
+      clusters:         :read_cluster,
       labels:           :read_label,
       issues:           :read_issue,
       project_members:  :read_project_member,

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

@@ -189,11 +189,11 @@
                   %span
                     Charts
 
-            -# - if project_nav_tab? :clusters TODO @shinya @ayufan
-            = nav_link(controller: :clusters) do
-              = link_to project_clusters_path(@project), title: 'Clusters', class: 'shortcuts-clusters' do
-                %span
-                  Clusters
+            - if project_nav_tab? :clusters
+              = nav_link(controller: :clusters) do
+                = link_to project_clusters_path(@project), title: 'Clusters', class: 'shortcuts-clusters' do
+                  %span
+                    Clusters
 
       - if project_nav_tab? :wiki
         = nav_link(controller: :wikis) do