Log information about StatefulSets as they are created, updated and deleted

[charleskorn]

This PR adds extra logging to rollout-operator to aid in reconstructing the series of events that affected a StatefulSet.

This is useful when trying to debug the behaviour of a StatefulSet. For example, we recently had an issue where a StatefulSet was deleted and was recreated with fewer replicas than expected, and this kind of logging would have been helpful to understand what happened.

Sample logs:

level=debug ts=2024-11-29T02:54:15.199822428Z msg="observed StatefulSet added" name=test-app namespace=rollout-operator-development replicas=5 generation=1 creation_timestamp=2024-11-29T02:54:15Z
level=debug ts=2024-11-29T02:54:50.2751915Z msg="observed StatefulSet updated" name=test-app namespace=rollout-operator-development old_replicas=5 new_replicas=7 old_generation=1 new_generation=2
level=debug ts=2024-11-29T02:55:20.447203583Z msg="observed StatefulSet deleted" name=test-app namespace=rollout-operator-development replicas=7 generation=2