Fix: attachment name for incoming messages

Use original_filename to get the name of the file attached to the message.

Had to add the message_type method to the WhatsApp/incoming_message_service due to the Assignment Branch Condition linter error for the attach_files method.

Fixes #4183

app/services/sms/incoming_message_service.rb

@@ -87,7 +87,7 @@ class Sms::IncomingMessageService
         file_type: file_type(attachment_file.content_type),
         file: {
           io: attachment_file,
-          filename: attachment_file,
+          filename: attachment_file.original_filename,
           content_type: attachment_file.content_type
         }
       )