Bug [3.1.3] FetchCompleted API is buggy

RemoteConfigService.Instance.FetchCompleted is kind of buggy that will block other operation from running properly. For my case it will make Addressables failed to instantiate game object properly when both are running at the same time. From what observed, it's caused by the API is not implemented running at main thread only and there's a one second Task delay. This API needs to be changed to main thread only solve a lot of similar issues caused by this remote config API since at Unity Monobehaviour environment is main thread. At a couple of previous preview version, it's working perfectly until a version that starting to behavior like that. I believe it's the version of remote config starts to use non-main thread API.