feat(apiserver): refactor the hooking mechanism for standalone apiserver (#93001)

It now uses a full build handler chain that can be passed from up top to `SetupConfig`.

Co-authored-by: Charandas Batra <charandas.batra@grafana.com>

pkg/services/apiserver/builder/request_handler.go

@@ -13,7 +13,7 @@ type requestHandler struct {
 	router *mux.Router
 }
 
-func getAPIHandler(delegateHandler http.Handler, restConfig *restclient.Config, builders []APIGroupBuilder) (http.Handler, error) {
+func GetCustomRoutesHandler(delegateHandler http.Handler, restConfig *restclient.Config, builders []APIGroupBuilder) (http.Handler, error) {
 	useful := false // only true if any routes exist anywhere
 	router := mux.NewRouter()