Parameter to put ssm-user in /etc/sudoers.d/ssm-users

[DarwinJS]

I'm finding the process of providing a custom bootstrap script just to restore the ssm-user to sudoers after this change Passwordless SUDO from ssm-user no longer supported to be excessively complex.

• The parameter description is inadequate: https://github.com/aws-quickstart/quickstart-amazon-eks/issues/417
• The existing bootstrap script must be forked and is complex just to add one command
• The bootstrapping of the bastion involves an entire library of bash code downloading as git repo

[tlindsay42]

Implemented this in EKS first in https://github.com/aws-quickstart/quickstart-amazon-eks/pull/471, and duplicating the implementation for the same reasons (reference).