FIX: include topic link when inviting existing users to a topic/PM

FEATURE: allow staff to use topic_url for customizing email template

app/mailers/user_notifications.rb

@@ -566,7 +566,8 @@ class UserNotifications < ActionMailer::Base
         topic_title: gsub_emoji_to_unicode(title),
         topic_excerpt: topic_excerpt,
         site_title: SiteSetting.title,
-        site_description: SiteSetting.site_description
+        site_description: SiteSetting.site_description,
+        topic_url: post.topic.url
       )
 
       html = PrettyText.cook(message, sanitize: false).html_safe

config/locales/server.en.yml

@@ -3152,7 +3152,7 @@ en:
     invited_group_to_private_message_body: |
       %{username} invited @%{group_name} to a message
 
-      > **%{topic_title}**
+      > **[%{topic_title}](%{topic_url})**
       >
       > %{topic_excerpt}
 
@@ -3160,10 +3160,14 @@ en:
 
       > %{site_title} -- %{site_description}
 
+      To join the message, click the link below:
+
+      %{topic_url}
+
     invited_to_private_message_body: |
       %{username} invited you to a message
 
-      > **%{topic_title}**
+      > **[%{topic_title}](%{topic_url})**
       >
       > %{topic_excerpt}
 
@@ -3171,10 +3175,14 @@ en:
 
       > %{site_title} -- %{site_description}
 
+      To join the message, click the link below:
+
+      %{topic_url}
+
     invited_to_topic_body: |
       %{username} invited you to a discussion
 
-      > **%{topic_title}**
+      > **[%{topic_title}](%{topic_url})**
       >
       > %{topic_excerpt}
 
@@ -3182,6 +3190,10 @@ en:
 
       > %{site_title} -- %{site_description}
 
+      To join the discussion, click the link below:
+
+      %{topic_url}
+
     user_invited_to_private_message_pm_group:
       title: "User Invited Group to PM"
       subject_template: "[%{email_prefix}] %{username} invited @%{group_name} to a message '%{topic_title}'"