feat: Send MMS through Twilio Inbox (#2959)

Send MMS message to customer for Twilio integration inbox.

Fixes #2311

spec/services/twilio/send_on_twilio_service_spec.rb

@@ -77,5 +77,20 @@ describe Twilio::SendOnTwilioService do
 
       ::Twilio::SendOnTwilioService.new(message: message).perform
     end
+
+    it 'if outgoing message has attachment and is for sms' do
+      # check for message attachment url
+      allow(messages_double).to receive(:create).with(hash_including(media_url: [anything])).and_return(message_record_double)
+      allow(message_record_double).to receive(:sid).and_return('1234')
+
+      message = build(
+        :message, message_type: 'outgoing', inbox: twilio_inbox, account: account, conversation: conversation
+      )
+      attachment = message.attachments.new(account_id: message.account_id, file_type: :image)
+      attachment.file.attach(io: File.open(Rails.root.join('spec/assets/avatar.png')), filename: 'avatar.png', content_type: 'image/png')
+      message.save!
+
+      ::Twilio::SendOnTwilioService.new(message: message).perform
+    end
   end
 end