DynamoDB global tables using CloudFormation
If you want to do it through cloudformation, you can do so using custom resources. It is pretty straight forward and easy to use. You can use their createGlobalTable API in your custom resource.
DynamoDB Global Table was introduced during the late 2017. Yes, as you mentioned, you can create the global tables using the AWS console or AWS CLI.
However, creating the global table using cloudformation template is yet to be available.
Meanwhile, please use the console or AWS CLI to create dynamodb global table.