FEATURE: Use group SMTP job and mailer instead of UserNotifications change (#13489)

This PR backtracks a fair bit on this one https://github.com/discourse/discourse/pull/13220/files.

Instead of sending the group SMTP email for each user via `UserNotifications`, we are changing to send only one email with the existing `Jobs::GroupSmtpEmail` job and `GroupSmtpMailer`. We are changing this job and mailer along with `PostAlerter` to make the first topic allowed user the `to_address` for the email and any other `topic_allowed_users` to be the CC address on the email. This is to cut down on emails sent via SMTP, which is subject to daily limits from providers such as Gmail. We log these details in the `EmailLog` table now.

In addition to this, we have changed `PostAlerter` to no longer rely on incoming email email addresses for sending the `GroupSmtpEmail` job. This was unreliable as a user's email could have changed in the meantime. Also it was a little overcomplicated to use the incoming email records -- it is far simpler to reason about to just use topic allowed users.

This also adds a fix to include cc_addresses in the EmailLog.addressed_to_user scope.

lib/email/message_builder.rb

@@ -140,7 +140,8 @@ module Email
         subject: subject,
         body: body,
         charset: 'UTF-8',
-        from: from_value
+        from: from_value,
+        cc: @opts[:cc]
       }
 
       args[:delivery_method_options] = @opts[:delivery_method_options] if @opts[:delivery_method_options]
@@ -161,11 +162,24 @@ module Email
       # please, don't send us automatic responses...
       result['X-Auto-Response-Suppress'] = 'All'
 
-      if allow_reply_by_email? && !@opts[:use_from_address_for_reply_to]
-        result[ALLOW_REPLY_BY_EMAIL_HEADER] = true
-        result['Reply-To'] = reply_by_email_address
-      else
+      if !allow_reply_by_email?
+        # This will end up being the notification_email, which is a
+        # noreply address.
         result['Reply-To'] = from_value
+      else
+
+        # The only reason we use from address for reply to is for group
+        # SMTP emails, where the person will be replying to the group's
+        # email_username.
+        if !@opts[:use_from_address_for_reply_to]
+          result[ALLOW_REPLY_BY_EMAIL_HEADER] = true
+          result['Reply-To'] = reply_by_email_address
+        else
+          # No point in adding a reply-to header if it is going to be identical
+          # to the from address/alias. If the from option is not present, then
+          # the default reply-to address is used.
+          result['Reply-To'] = from_value if from_value != alias_email(@opts[:from])
+        end
       end
 
       result.merge(MessageBuilder.custom_headers(SiteSetting.email_custom_headers))

lib/email/sender.rb

@@ -429,6 +429,8 @@ module Email
     end
 
     def set_reply_key(post_id, user_id)
+      # ALLOW_REPLY_BY_EMAIL_HEADER is only added if we are _not_ sending
+      # via group SMTP and if reply by email site settings are configured
       return if !user_id || !post_id || !header_value(Email::MessageBuilder::ALLOW_REPLY_BY_EMAIL_HEADER).present?
 
       # use safe variant here cause we tend to see concurrency issue