add optional delegate in UpdateUserAsync that lets you update any cached/session info as well

[adamfoneil]

There's already an OnUserUpdatedAsync delegate, but if not initialized, then you can't call it. So, issue is to make this easier to call.

The use case here is I've updated some user property in the database, but I need to make sure it's reflected in Session (or wherever I've cached it).

I think maybe a new optional argument on the AddDapperCX startup method makes sense.