add strict_missing_exception

assign: @amygdalama 

This allows client code to override NotFoundError for strict_missing.

It's not that great of an interface (I'd prefer to take a function that can return in place of the patch), but it'll solve our problem.
This behavior (turned off + provided an exception -> nothing happens) lines up with my [pedantic] reading of the docs, haha.

Maybe overloading the option would be better? strict_missing would take False (default, no action), True (NotFoundError), or an exception (which would be raised instead of NotFoundError).