Improve LeakDetector

HDDS-9528 introduces a leak detector framework.

Possible improvements:

• simplify managed objects by moving getStackTrace() into track() (need to skip +1 level in formatStackTrace() (this is done as part of HDDS-9528)
• let LeakTracker implement AutoCloseable Closeable and change methods that return it to use the interface
• distinguish detectors with the same name by appending a unique integer
• split two test cases in TestLeakDetector