OF-3306: Reduce memory footprint of Pubsub subscription
The issue in OF-3306 relates to a large amount of `NodeSubscription` instances being loaded in memory. This commit does not address that, but does significantly reduce the memory footprint of each instance. This helps reduce the impact of the issue.
The memory footprint is reduced by switching from a Logger-instance per instance, to a static one that's shared with all instances.
In one heap dump that was analyzed, these Logger instances accounted for (very roughly) 15% of the heap size.
(cherry picked from commit c17dbbb567b64d9e283ece1b7b0419afb5e9a204)
