feat: Sort contacts via name, email, phone_number, last_activity_at (#1870)

db/migrate/20210306170117_add_last_activity_at_to_contacts.rb

@@ -0,0 +1,22 @@
+class AddLastActivityAtToContacts < ActiveRecord::Migration[6.0]
+  def up
+    # rubocop:disable Rails/SkipsModelValidations
+    add_column :contacts, :last_activity_at, :datetime, index: true, default: nil
+    Conversation.find_in_batches do |conversation_batch|
+      conversation_batch.each do |conversation|
+        contact = conversation.contact
+        if contact.last_activity_at.nil? || conversation.updated_at > contact.last_activity_at
+          contact.update_columns(last_activity_at: conversation.updated_at)
+        end
+      end
+    end
+
+    Contact.where(additional_attributes: nil).update_all(additional_attributes: {})
+    Contact.where(phone_number: '').update_all(phone_number: nil)
+    # rubocop:enable Rails/SkipsModelValidations
+  end
+
+  def down
+    remove_column :contacts, :last_activity_at, :datetime, index: true, default: nil
+  end
+end