ABC-90 Add POST /emoji/search and GET /emoji/autocomplete API endpoints (#8125)

* Add POST /emoji/search and GET /emoji/autocomplete API endpoints

* Add constant to be clearer

api4/api.go

@@ -184,7 +184,7 @@ func Init(a *app.App, root *mux.Router, full bool) *API {
 	api.BaseRoutes.DataRetention = api.BaseRoutes.ApiRoot.PathPrefix("/data_retention").Subrouter()
 
 	api.BaseRoutes.Emojis = api.BaseRoutes.ApiRoot.PathPrefix("/emoji").Subrouter()
-	api.BaseRoutes.Emoji = api.BaseRoutes.Emojis.PathPrefix("/{emoji_id:[A-Za-z0-9]+}").Subrouter()
+	api.BaseRoutes.Emoji = api.BaseRoutes.ApiRoot.PathPrefix("/emoji/{emoji_id:[A-Za-z0-9]+}").Subrouter()
 
 	api.BaseRoutes.ReactionByNameForPostForUser = api.BaseRoutes.PostForUser.PathPrefix("/reactions/{emoji_name:[A-Za-z0-9\\_\\-\\+]+}").Subrouter()