Chore: Convert Message Sender to polymorphic (#740)

Fixes #680

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

@@ -4,7 +4,8 @@ class Api::V1::Accounts::Conversations::MessagesController < Api::V1::Accounts::
   end
 
   def create
-    mb = Messages::Outgoing::NormalBuilder.new(current_user, @conversation, params)
+    user = current_user || @resource
+    mb = Messages::Outgoing::NormalBuilder.new(user, @conversation, params)
     @message = mb.perform
   end
 

app/controllers/api/v1/widget/messages_controller.rb

@@ -45,7 +45,7 @@ class Api::V1::Widget::MessagesController < Api::V1::Widget::BaseController
   def message_params
     {
       account_id: conversation.account_id,
-      contact_id: @contact.id,
+      sender: @contact,
       content: permitted_params[:message][:content],
       inbox_id: conversation.inbox_id,
       message_type: :incoming