Returns the DashboardUserContext for the logged-in administrator, plus a flag which is false while Administrator custom fields are still loading.
readyCallers must not evaluate user-dependent rules until ready is true, otherwise
rules that read customFields will briefly see them absent.
Must be called inside ChannelProvider, which sits inside AuthProvider. Login
extensions render outside both and cannot use this hook.
Parameters
DashboardUserContextOptionsOptions for useDashboardUserContext.