Consider adding a global enabled/disabled flag to swiftly cease performing updates

**Issue or Feature Request:**

It would be useful if there was some sort of andon-cord-style command which could prevent Brupop from performing any additional actions. The imagined use-case is that a Bottlerocket update has unintended consequences for a customer application, and technicians would need a fast mechanism for disabling further updates.

**Workarounds**
You can currently achieve similar behavior by removing brupop's label (`bottlerocket.aws/updater-interface-version=2.0.0`) from all nodes, though this is much less ergonomic.