Message Customizations

https://docs.aws.amazon.com/cognito/latest/developerguide/signing-up-users-in-your-app.html
https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-pool-settings-message-customizations.html
https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-identity-pools-working-with-aws-lambda-triggers.html#cognito-user-pools-lambda-trigger-syntax-custom-message
https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-settings-attributes.html
https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-settings-email-phone-verification.html