JMH: GC profiler options

GC profiler has two large parts: measuring allocs and measuring churn. Churn measurement was the first thing implemented in this profiler, and then allocation measurement was added. At this point, churn is seldom used for performance benchmarks, as it is noisy. Additionally, it depends on asynchronous GC notifications, and thus introduces iteration delays to catch up with them.

We can add options to GC profiler and turn off "churn" by default.