use light email template for staged users

app/mailers/user_notifications.rb

@@ -289,7 +289,10 @@ class UserNotifications < ActionMailer::Base
     end
 
     template = "user_notifications.user_#{notification_type}"
-    template << "_pm" if post.topic.private_message?
+    if post.topic.private_message?
+      template << "_pm"
+      template << "_staged" if user.staged?
+    end
 
     email_opts = {
       topic_title: title,

config/locales/server.en.yml

@@ -1916,6 +1916,22 @@ en:
 
         Please visit this link to view the message: %{base_url}%{url}
 
+    user_invited_to_private_message_pm_staged:
+      subject_template: "[%{site_name}] %{username} invited you to a message '%{topic_title}'"
+      text_body_template: |
+
+        %{username} invited you to a message
+
+        > **%{topic_title}**
+        >
+        > %{topic_excerpt}
+
+        at
+
+        > %{site_title} -- %{site_description}
+
+        Please visit this link to view the message: %{base_url}%{url}
+
     user_invited_to_topic:
       subject_template: "[%{site_name}] %{username} invited you to a topic '%{topic_title}'"
       text_body_template: |
@@ -2004,6 +2020,15 @@ en:
         ---
         %{respond_instructions}
 
+    user_posted_pm_staged:
+      subject_template: "%{optional_re}%{topic_title}"
+      text_body_template: |
+
+        %{message}
+
+        ---
+        %{respond_instructions}
+
     digest:
       why: "A brief summary of %{site_link} since your last visit on %{last_seen_at}"
       subject_template: "[%{site_name}] Digest"