Previously, we used a simple boolean to track the state of the package updates,
and didn't reset it back when the config validation was successful because it was
assumed that if we successfully validated the config beforehand, then the worker
would also successfully reload the config afterwards, and that the old worker would
be terminated. However, this assumption is not always true due to a number of reasons
that I can't even think of right now, but the most obvious one is that after we successfully
validated the config, the config  might have changed again before the worker was able
to reload it. If that happens, then the new worker might fail to successfully validate
the config due to the recent changes, in which case the old worker would remain active,
and this flag would still be set to true, causing any subsequent requests to fail with a
`423` until you manually restart the Icinga 2 service.

So, in order to prevent such a situation, we are additionally tracking the last time a reload
failed and allow to bypass the `m_RunningPackageUpdates` flag only if the last reload failed
time was changed since the previous request.