VSI: Lower pt of associated tracks in VSI_BoostedMuons

This MR contains an addition to the VSI_BoostedMuons configuration that was recently added to the LLP1 derivation (!75842 (merged)). The VSI_BoostedMuons configuration is optimised for the reconstruction of muons with large displacement, but small d0-values, typical for boosted long-lived particle signatures. This is developed in the context of the low-mass dimuon analysis ANA-EXOT-2024-18 and might also be interesting for other analyses in the LUP group.

The new addition lowers the pT threshold of tracks that are attached to the secondary vertex in the track-association step of VSI. This threshold is set to 1000 MeV by default and is now lowered to 500 MeV for VSI_BoostedMuons. The change is steered by the associatePtCut flag in the VSI configuration.

The purpose of these changes is to include more low-pT tracks to aid the background characterisation for the low-mass dimuon analysis.

The changes have been validated in data and signal. For details see the presentation from the Low-mass dimuon analysis meeting on 10 February 2024.There is no increase in disk usage for the DAOD_LLP1 following this change.

Tagging @spagan @kbai @mamirono @jburzyns @csebasti @kdipetri