Billing Group Flat Custom Line Item

This template creates a flat charge custom line item of $10 attached to a billing group. The custom line item is created through CloudFormation and has a description of 'Test flat custom line item created through CloudFormation for a $10 charge.' The billing group ARN is obtained using the `Fn::GetAtt` function. The custom line item charge details specify a flat charge value of 10 and a type of 'FEE'. The billing period range is set to start in November 2022.