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Heads up for anyone still wanting to do this for their tenant; I stumbled over an excellent article which covers using a json file for all new provisioned sites/groups/teams:
This is ridiculous... why is there no global config? Please add it to the Teams admin console at least...
This also needs to be an option under Teams Admin settings on o365. Until I found a json script a few hours ago this wasn't even possible for pre-provisioned Groups which use predefined templates.