User/martyniu/21.9 trig htt memory fixes

There were some memory issues running the HTTSim code which only became apparent when running on mu=200 files.

These fixes improve the situation by reserving memory for large vectors before they are filled so that they don't increase on the fly. It also removes a memory leak in the storage of the truth information.

These changes have been taken from the atlas-tdaq-htt fork of athena which is not ready to be merged as a whole.