Currently if a consumer of the addons api (e.g. addons-frontend) wants to filter by all add-ons that are supposed to badged (exposed as being reviewed by Mozilla) it has to know which promoted groups have that property and then specify all of those groups as ?promoted=recommended,verified,sponsored,line. If we have a ?promoted=badged filter then the consumer of the api can make a simpler query that isn't dependent on identical logic being maintained on addons-server and addons-frontend.