Remove async registration of apiWatchers, since it breaks discovering `role: endpoints` and `role: endpointslices` targets,
which depend on pod and service objects.
There is no need in reloading `endpoints` and `endpointslices` targets if the referenced `pod` or `service` objects change,
since in this case the corresponding `endpoints` and `endpointslices` objects should also change because they contain
ResourceVersion of the referenced `pod` or `service` objects, which is modified on object update.
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1182
fe084fdd33