Allow for namespace creation without RBAC roles

[pete0emerson]

The create_resources variable controls both the namespace creation and the RBAC role creation. What if I want to create the namespace without the roles?

I've described a workaround in https://github.com/orgs/gruntwork-io/discussions/722 (regarding the service catalog and reference architecture patterns), but allowing separate control of namespace and namespace-roles may be cleaner.

I'm not sure how often a situation like this comes up, but thought it worth adding a ticket for triaging.