PWGMM/Mult/Tasks/heavy-ion-mult.cxx: Add particle species+weak decay … (AliceO2Group#7904)

Major changes:
- add two process functions
1. processMCfillspecies => to study eta dist of different particle species 
2. processStrangeYield => to study the mass distributions of strange particles (K0s, lambda, anti-lambda)

Minor changes:
- add template functions for track selection (avoid writing similar track conditions in all process functions)
- remove some of the histograms which are not necessary

Author: abmodak