Support adding a PermissionsBoundary to IAM Roles created from clusterawsadm bootstrap iam create-cloudformation-stack

[mmb]

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Due to security requirements I need IAM roles to have an attached PermissionsBoundary. I propose to add an optional permissionsBoundary field to the bootstrap config that accepts a single PermissionsBoundary ARN and adds it to all IAM roles created as part of the CloudFormation stack.

I have a straightforward working patch for this and can submit a PR if it would be considered.

See also #2117