Per request middleware options
Currently, maxFileSize is a fixed value. However, the graphql server might have different upload operations that have different size allowances. 
While it's certainly possible to check the stream data length in a resolver, it would be nice if the maxFileSize option could be a function that receives the operation name and variables and and returns a maxFileSize. This should work because the operation is parsed before the multipart data is read.

What do you think about this? 