Where can I find settings for app review requests?
In iOS 10.3, this has been removed, though it was present in the beta. 

However, there is hope!

Using the API (which will probably be the only allowed method for review requests going forward), developers can only schedule up to 3 review requests in a 365 day period. 
Source: Apple Insider

This will lead to virtually no nagging, and it is rumored that Apple will stop accepting apps that ask for ratings using any other means shortly. 

Though it is unfortunate that there is no switch to disable rating requests, this is definitely a step in the right direction, for both developers and users.