Draft: Added new files for tau2KS0mu and tau2KS0KS0mu decays (from b quarks)

(Updated) MR related to the implementation of two new DecFiles to simulate the following LFV tau decays:

EventType	Decay chain
31113148	b\to \tau\to K_s^{0}(\pi^+\pi^-)\mu
31115149	b\to \tau\to K_s^{0}(\pi^+\pi^-)K_s^{0}(\pi^+\pi^-)\mu

Each DecFile implements generator-level selections on GP, GPT, GTHETA of the final state particles and a selection on the presence of a b quark among the \tau ancestors, based on the required decay chain.