It would be really useful to be able to selectively filter logging so that we can get more info about a particular cluster (or more generally a particular CR), and carry on logging the rest normally. I think this can be done using log4j2 Markers. Specifically I think each namespace would correspond to a Marker, and each CR in that namespace a child Marker (or maybe a single ns/name marker), and we could store a Marker in a Reconciliation, which we pass around widely already for logging purposes. Log4j2 can filter using markers.

Note: we can't use the DynamicThresholdFilter filtering which uses a ThreadContext-bound map because Vertx means that we jump around between threads all the time.

Started by #4653