Update interface GMM logic tree
Once bias-corrected versions of the Alaska interface GMMs are implemented (see ghsc/nshmp/nshmp-lib#217 (closed)), update logic tree with 1/6 weight on the three published models and their corrected counterparts:
AG_20_GLOBAL_INTERFACEKBCG_20_GLOBAL_INTERFACEPSBAH_20_ALASKA_INTERFACEAG_20_GLOBAL_INTERFACE_AK_BIAS_CORRKBCG_20_GLOBAL_INTERFACE_AK_BIAS_CORRPSBAH_20_ALASKA_INTERFACE_AK_BIAS_CORR