ConcurrencyMode is missing from StackSet OperationPreferences

[cs-matti]

The StackSet OperationPreferences should include a parameter called ConcurrencyMode. This parameter is missing from the goformation StackSet_OperationPreferences structure.

https://github.com/awslabs/goformation/blob/master/cloudformation/cloudformation/aws-cloudformation-stackset_operationpreferences.go

https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_StackSetOperationPreferences.html

ConcurrencyMode
Specifies how the concurrency level behaves during the operation execution.