Added new decfiles for Ds2taunu,tau2KS0mu and tau2KS0KS0mu decays

MR related to the implementation of 4 new DecFiles to simulate the following LFV tau decays:

EventType	Decay chain
23513128	c\to D_{s}\to\tau\nu_\tau,\;\tau\to K_s^{0}(\pi^+\pi^-)\mu
23513129	b\to D_{s}\to\tau\nu_\tau,\;\tau\to K_s^{0}(\pi^+\pi^-)\mu
23515130	c\to D_{s}\to\tau\nu_\tau,\;\tau\to K_s^{0}(\pi^+\pi^-)K_s^{0}(\pi^+\pi^-)\mu
23515131	b\to D_{s}\to\tau\nu_\tau,\;\tau\to K_s^{0}(\pi^+\pi^-)K_s^{0}(\pi^+\pi^-)\mu

MR related to !2117