awaitLogIn
This function will change the current appUserID. Typically this would be used after a log out to identify a new user without calling configure
Coroutine friendly version of Purchases.logIn.
Return
The CustomerInfo associated to the current user.
Parameters
appUserID
The new appUserID that should be linked to the currently user
Throws
with a PurchasesError if there's an error login the customer info.