Add lock and grey out subscribers tab

[PREMIUM-225]

mailpoet/assets/css/src/components-automation-analytics/tabs/orders.scss

@@ -1,7 +1,8 @@
 @import '../colors';
 @import 'mixins';
 
-.mailpoet-analytics-tab-orders {
+.mailpoet-analytics-tab-orders,
+.mailpoet-analytics-tab-subscribers {
   color: $color-gutenberg-grey-600;
 }
 

mailpoet/assets/js/src/automation/integrations/mailpoet/analytics/components/tabs/index.tsx

@@ -48,7 +48,11 @@ export function Tabs(): JSX.Element {
     tabs.push({
       name: 'automation-subscribers',
       className: 'mailpoet-analytics-tab-subscribers',
-      title: __('Subscribers', 'mailpoet'),
+      title: (
+        <>
+          {__('Subscribers', 'mailpoet')} <Icon icon={lockSmall} />
+        </>
+      ) as unknown as string,
     });
   }