Allow changing default options for express.json() middleware

I've ran into an issue where the default body size limit of 100kb (https://expressjs.com/en/api.html#express.methods) is too small for my usecase. Especially when trying to send a file - the middleware always returns the PayloadTooLargeError error.

It would be nice if there was a way to provide custom configuration to the express.json middleware.
