fix(mobile/navigations) added LoadConfigOverlay to RootNavigator (#11067)
Converted LoadConfigOverlay to a JitsiScreen component that right now is part of navigation as ConnectingPage, plus I
separated appNative and other actions into web and native.
fix(rn,navigation) fix navigating back to the welcome page
The CONFERENCE_WILL_LEAVE reducer in base/conference wipes the state so
we cannot rely on the old room value.
We may want to revisit this in the future.