Add finalize() messages indicating result of systematics regex filtering

@tadej @krumnack

I found this useful for feedback when building some systematics filtering features for an analysis framework -- more direct feedback than checking a tree or the systlist histogram. It seems always useful in the dumper alg, but it only outputs when there is a non-trivial filter in the service.

I do wonder if the systematics list is better written in a tiny metadata tree instead?