Per [discussion here](https://gitlab.com/gitlab-com/gl-infra/production/-/issues/1898#note_318576770), in addition to intercepting calls to chef-client when it's disabled, we would also like to be able to easily check whether or not it is disabled. Add a `chef-client-is-enabled` script to the `gitlab-server::chef-client-disabler` recipe. Expected behavior: * If chef-client is enabled, this script will say so and exit 0. * If chef-client is disabled, this script will exit non-zero and show when, by whom, and for what reason (i.e. same output as though chef-client had been run and intercepted).