Improve RLS policies for template data The removed POLICY manage_templates missed a WITH CHECK (true), because the USING clause is applied to new rows, too, if no WITH CHECK is provided, thus implying a dead-lock situation with the FK constraint on user_templates (the POLICY requiring a row in user_templates while INSERTing such row requires a row in templates). New POLICY on user_templates prevents waterway_admin from relating templates to users from other countries and allows to write other policies more compact.