Deprecate/remove resource_types endpoint

This is an epic to cover the work of deprecating / removing the old resource_types endpoint from Puppet Server.

The first step of this is going to be to work with eric.sorenson and start a thread on one of the public mailing lists to try to determine what (if any) other use cases for it that we need to be able to support, beyond the functionality that will be available in the new environment_classes endpoint.