title: Fail to create a custom domain name for websocket API gateway using AWS Cloudformation
body: <p>I need to create a custom domain name for a websocket enabled API gateway and seems that CloudFormation for API gateway v2 (which is basically for websocket) doesn’t support it (at least the documentation  <a href="https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/cfn-reference-apigatewayv2.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/cfn-reference-apigatewayv2.html</a>  doesn’t mention this). I tried with <code>AWS::ApiGateway::DomainName</code> which I believe is for Rest API gateway but the stack fails with the error</p>
  
  <blockquote>
    <p>This custom domain name cannot map to WEBSOCKET protocol Apis.</p>
  </blockquote>
  
  <p>I see that AWS CLI does support API gateway v2 create domain name command (<a href="https://docs.aws.amazon.com/cli/latest/reference/apigatewayv2/create-domain-name.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/cli/latest/reference/apigatewayv2/create-domain-name.html</a>) but not sure the reason why the CloudFormation wouldn’t support this.</p>
  
  <p>Any workaround or feedback would be greatly appreciated.</p>