feat: Support Twilio Messaging Services (#4242)

This allows sending and receiving from multiple phone numbers using Twilio messaging services

Fixes: #4204

app/views/api/v1/models/_inbox.json.jbuilder

@@ -45,6 +45,7 @@ if resource.facebook?
 end
 
 ## Twilio Attributes
+json.messaging_service_sid resource.channel.try(:messaging_service_sid)
 json.phone_number resource.channel.try(:phone_number)
 json.medium resource.channel.try(:medium) if resource.twilio?