JetForwardJvtTool: Add flag to read in instead of calculate fJVT
This allows the JetForwardJvtTool to be used on DAOD's in release 22 where Track MET is not stored but the fJVT for primary vertex is.
This allows the JetForwardJvtTool to be used on DAOD's in release 22 where Track MET is not stored but the fJVT for primary vertex is.