Enhancement - Allow Vanadis to Start and Stop Stat Collection for Code Region of Interest

[plafratt]

New Issue for sst-elements

1 - Detailed description of problem or enhancement

According to a comment on #2189, Ariel allows starting and stopping the collection of stats in a code region of interest through calling a dummy function. Having this feature available in Vanadis would be very useful. There was a request in the comment on #2189 for me to file an enhancement request for this feature.