Ensure instance stats links behave correctly

Instance statistics links should only be displayed when the features are
available for a user.

We need to seperate the logic for instance statistics and analytics.

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

-- return unless dashboard_nav_link?(:analytics)
+- return unless can?(current_user, :read_instance_statistics)
 = nav_link(controller: :dev_ops_score) do
   = link_to instance_statistics_dev_ops_score_index_path do
     .nav-icon-container

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

@@ -40,6 +40,10 @@ describe 'layouts/nav/sidebar/_analytics' do
       end
 
       context 'and user has access to instance statistics features' do
+        before do
+          allow(view).to receive(:can?) { true }
+        end
+
         it 'has `DevOps Score` link' do
           render
 
@@ -58,9 +62,11 @@ describe 'layouts/nav/sidebar/_analytics' do
       end
 
       context 'and user does not have access to instance statistics features' do
-        it 'no instance statistics links are rendered' do
-          allow(view).to receive(:dashboard_nav_link?).and_return(false)
+        before do
+          allow(view).to receive(:can?) { false }
+        end
 
+        it 'no instance statistics links are rendered' do
           render
 
           expect(rendered).not_to have_content('DevOps Score')
@@ -78,6 +84,10 @@ describe 'layouts/nav/sidebar/_analytics' do
       end
 
       context 'and user has access to instance statistics features' do
+        before do
+          allow(view).to receive(:can?) { true }
+        end
+
         it 'has `DevOps Score` link' do
           render
 
@@ -96,9 +106,11 @@ describe 'layouts/nav/sidebar/_analytics' do
       end
 
       context 'and user does not have access to instance statistics features' do
-        it 'no instance statistics links are rendered' do
-          allow(view).to receive(:dashboard_nav_link?).and_return(false)
+        before do
+          allow(view).to receive(:can?) { false }
+        end
 
+        it 'no instance statistics links are rendered' do
           render
 
           expect(rendered).not_to have_content('DevOps Score')