title: Updating user pool schema is not allowed from cloudformation
body: <p>I am trying to make phone_number mutable through cloudformation templete, but getting below error </p>
  
  <p>"Updating user pool schema is not allowed from cloudformation. Use the AddCustomAttributes API or the AWS Cognito Console to update user pool schema."</p>
  
  <p>Below is my schema snippet:-</p>
  
  <pre><code>      {
          "Name": "phone_number",
          "AttributeDataType": "String",
          "Mutable": true,
          "Required": true
        },
  </code></pre>
  
  <p>Not sure why cloudformation is not able to update the UserPoolId.</p>