Add default GTM config key
Add default GTM config key

Add the key for GTM and blank default value into the DEFAULT_CONFIG

saimn/sigal,t-animal/sigal,jasuarez/sigal,xouillet/sigal,jasuarez/sigal,jasuarez/sigal,saimn/sigal,t-animal/sigal,xouillet/sigal,saimn/sigal,t-animal/sigal,xouillet/sigal