Add Instance class to list admin records (#3443)

app/models/instance.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class Instance
+  include ActiveModel::Model
+
+  attr_accessor :domain, :accounts_count
+
+  def initialize(account)
+    @domain = account.domain
+    @accounts_count = account.accounts_count
+  end
+end