Update MET systematics tool default to the latest TST recommendations

Follow up from mattermost discussion, update default value for the MET systematic tool to point to latest MET TST recommendations (see also https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/EtmissRecommendationsFullRun2#Track_Soft_Term_TST_Systematics). This will be implicitly used by MET CP Algorithms, therefore applying latest recommendations to analysis level

Tagging @krumnack, @tstreble for CPAlg

Tagging @wbalunas and @cmorenom for MET group