EFTracking emulation: implemented LRT parametrized efficiency

Introduced an example function to parametrise the tracking efficiency versus d0 for the LRT scenario (requested by @anghosh) for EFTRACK-171. There are 2 options to use either a step function (commented out for now) or a double Fermi function with 3 steps at 1, 0.8 and 0.2, to follow the behaviour of Figure 2.11 in the TDR amendment (https://cds.cern.ch/record/2802799/files/ATLAS-TDR-029-ADD-1.pdf) - attached. I also attach the curve generated with the current parameterization and stored in effLRT_functions_vs_d0 within the smearing framework.

The flex points can be changed by JO with smearedTrackEfficiency_d0low_LRT and smearedTrackEfficiency_d0high_LRT to emulate different scenarios.