chore: Add CSAT survey toggle attribute to Inboxes (#2455)

ref: #1890

db/migrate/20210618095823_add_csat_toggle_for_inbox.rb

@@ -0,0 +1,5 @@
+class AddCsatToggleForInbox < ActiveRecord::Migration[6.0]
+  def change
+    add_column :inboxes, :csat_survey_enabled, :boolean, default: false
+  end
+end