agent: define a sensible strategy for dealing with configuration errors.

[klihub]

It is quite clear how to deal with configuration delivery errors: keep retrying indefinitely and preferably propagate the fact of failed configuration back to the source, IOW to the ConfigMap.

It is not clear however how to deal with application-level configuration errors. The agent has no knowledge of the application/configuration semantics, neither it is in control or even gets notified about system configuration changes.