Limit how offten a threads dump will be saved

[mpapis]

Currently in each iteration when threads a re blocked we will save a dump, it should be possible to limit it with extra threshold, and it probably could be different then the one to check for how long thread was blocked.

Relevant lines:

• jvm-monitoring-agent/src/com/toptal/jvm/monitoring/Agent.java

  Line 109 in e22e410

  saveThreadsDump(threads);