Compute isolation quantities using Velo particles in Run3
Related to #494
Some Run2 analysis already proved the improvements brought by using isolation variables calculated using velo tracks instead of long ones.
For Run3, the algorithm implemented in Hlt2Line.isolation which persists the selection of extra particles using extra_outputs argument of Hlt2Line method requires a container of type LHCb::Particle and not LHCb::Track, therefore since VELO tracks have not yet mass hypothesis it is not possible so far to persist a selection of them to compute isolation quantities offline.
The issue works as a reminder to add to the current framework the isolation also for VELO particles once make_velo_* will be in standard_particles
The most straightforward way in the RD case could be add an input flag argument to the method select_parts_for_isolation named VeloTrackIso which uses make_velo_pions as extra_particles input.