Fix wrong type for gFEX MET coefficients

With this MR the type of the gFEX MET coefficients is changed to float.

Motivation: Although the MET coefficients are defined as integers in the Trigger Menu and represent the 10 bits values used in the firmware, in the simulation these values (retrieved from the Trigger Menu) need to be converted to floats in order to get meaningful results when combined with hard and soft MET terms. e.g MET_x is defined as MET_x = a*MHT_x + b*MST_x.