feat: Contactable Inboxes API (#2101)

- Add endpoint which lists inboxes through which a contact can be contacted
- Conversation creation API auto-creates contact_inbox for specific channels [ Twilio, email, api]
- Ability to send the initial message payload along with the conversation creation
- Fixes #1678 ( issue saving additional attributes for conversation )

app/controllers/api/v1/accounts/conversations/messages_controller.rb

@@ -4,7 +4,7 @@ class Api::V1::Accounts::Conversations::MessagesController < Api::V1::Accounts::
   end
 
   def create
-    user = current_user || @resource
+    user = Current.user || @resource
     mb = Messages::MessageBuilder.new(user, @conversation, params)
     @message = mb.perform
   rescue StandardError => e