When the MCO performs a cluster upgrade, there may be cases where a new operating system is not available. Despite this, the MCO will emit a pair of events, OSUpgradeStarted / OSUpdateStaged in close succession to one another. This obfuscates the fact that no OS upgrade actually occurred and can make someone believe that an OS upgrade took place when in fact it did not.

Instead, we should emit a clear event such as, NoOSUpgradeAvailable or OSUpgradeSkipped or similar to make it clear that no OS upgrade actually occurred during a cluster upgrade.

Additional context may be found in https://coreos.slack.com/archives/C02CZNQHGN8/p1633973677227800 as well as in https://bugzilla.redhat.com/show_bug.cgi?id=2012969.