FIX: Capture CC addresses for forwarded emails (#14254)

When forwarding emails into the group inbox, we now use the
original sender email as the from_address since
2ac9fd9dff. However, we have not
been saving the original CC addresses of the forwarded email,
which are needed to include those recipients in on the conversation
when replying via the group inbox.

This commit captures the CC addresses on the incoming email, and
makes sure the emails are created as staged users and added to the
list of topic allowed users so they are included on CC's sent by
the GroupSmtpEmail and other jobs.

lib/email/receiver.rb

@@ -143,13 +143,17 @@ module Email
     end
 
     def create_incoming_email
+      cc_addresses = Array.wrap(@mail.cc)
+      if has_been_forwarded? && embedded_email&.cc
+        cc_addresses.concat(embedded_email.cc)
+      end
       IncomingEmail.create(
         message_id: @message_id,
         raw: Email::Cleaner.new(@raw_email).execute,
         subject: subject,
         from_address: @from_email,
         to_addresses: @mail.to,
-        cc_addresses: @mail.cc,
+        cc_addresses: cc_addresses,
         imap_uid_validity: @opts[:imap_uid_validity],
         imap_uid: @opts[:imap_uid],
         imap_group_id: @opts[:imap_group_id],
@@ -956,7 +960,7 @@ module Email
       email, display_name = parse_from_field(embedded)
 
       if forwarded_by_address && forwarded_by_name
-        forwarded_by_user = stage_sender_user(forwarded_by_address, forwarded_by_name)
+        @forwarded_by_user = stage_sender_user(forwarded_by_address, forwarded_by_name)
       end
 
       return false if email.blank? || !email["@"]
@@ -985,10 +989,10 @@ module Email
                        post_type: post_type,
                        skip_validations: user.staged?)
         else
-          if forwarded_by_user
-            post.topic.topic_allowed_users.find_or_create_by!(user_id: forwarded_by_user.id)
+          if @forwarded_by_user
+            post.topic.topic_allowed_users.find_or_create_by!(user_id: @forwarded_by_user.id)
           end
-          post.topic.add_small_action(forwarded_by_user || user, "forwarded")
+          post.topic.add_small_action(@forwarded_by_user || user, "forwarded")
         end
       end
 
@@ -1324,7 +1328,11 @@ module Email
       if result.post
         @incoming_email.update_columns(topic_id: result.post.topic_id, post_id: result.post.id)
         if result.post.topic&.private_message? && !is_bounce?
-          add_other_addresses(result.post, user)
+          add_other_addresses(result.post, user, @mail)
+
+          if has_been_forwarded?
+            add_other_addresses(result.post, @forwarded_by_user || user, embedded_email)
+          end
         end
 
         # Alert the people involved in the topic now that the incoming email
@@ -1346,11 +1354,11 @@ module Email
       html
     end
 
-    def add_other_addresses(post, sender)
+    def add_other_addresses(post, sender, mail_object)
       %i(to cc bcc).each do |d|
-        next if @mail[d].blank?
+        next if mail_object[d].blank?
 
-        @mail[d].each do |address_field|
+        mail_object[d].each do |address_field|
           begin
             address_field.decoded
             email = address_field.address.downcase