Add ClusteringThresholds condition for UT
Follow up patch in addition to the recently merged ut_calib
branch (now deleted).
This MR is to port ClusteringThresholds.xml, which seems to be overlooked and will actually be accessed by UTTightDigitCreator.cpp in Boole. Without this condition, Boole cannot run with UT in DD4hep.
Edited by Hangyi Wu