Chore: Provide fixed attachment URLs for Channels (#4507)

Prior to this change, The attachment URL sent from Chatwoot to 3rd party integrations like Whatsapp and Facebook
involved a 301 redirect before the original content is served. This causes intermittent breakages for the sent attachments.

fixes: #3632
ref: https://blog.saeloun.com/2021/09/14/rails-7-adds-expiring-urls-to-active-storage.html

app/models/channel/telegram.rb

@@ -95,7 +95,7 @@ class Channel::Telegram < ApplicationRecord
       when 'file'
         telegram_attachment[:type] = 'document'
       end
-      telegram_attachment[:media] = attachment.file_url
+      telegram_attachment[:media] = attachment.download_url
       telegram_attachments << telegram_attachment
     end