chore(cfn): CUDly-CrossAccount PrimaryRoleName still defaults to the retired stack's role #1585

#1577 retired the CloudFormation install stack (D29). cloudformation/stacks/CUDly-CrossAccount is a target-account role template and stays. Its PrimaryRoleName parameter still defaults to CUDly-LambdaRole, the role the retired stack created. Terraform installs name the runtime role differently.

Owner decision: changing the default affects anyone who deploys the template without overriding it. Options:

• make it required, with no default;
• default it to the Terraform Lambda role's name;
• leave it and document it.

Found in review of #1577.