Add new purge_stack_instances parameter for the CloudFormation stack set module

[rmahroua]

SUMMARY

This PR extends the cloudformation_stack_set module by adding a purge_stack_instances module parameter. Currently, the module is not idempotent because removing an account from the list of accounts doesn't instruct CloudFormation to remove account instances from the stack set. This change ensures that CloudFormation keeps stack instances only for the accounts listed in the accounts list.

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

cloudformation_stack_set