Properly handle chef client disabling for runner fleet upgrades

As a follow-up for gitlab-cookbooks/cookbook-wrapper-gitlab-runner!27 (merged) let's use a proper way for disabling chef client.

The new way will not only disable the client but will also disable alerting and leave a notice about the reason, which will prevent unintended and unwanted re-enabling before the upgrade procedure is finished.

This MR should be merged immediately after gitlab-cookbooks/cookbook-wrapper-gitlab-runner!27 (merged) is and after the cookbook is updated in the chef-repo and on the Chef Server