I would recommend moving these to be under your own domain, at which point you can use something like Transform Rules.
You’ll currently be using the dedicated imagedelivery.net domain but all of your images are actually available under your website in the /cdn-cgi/imagedelivery path.
31536000 translates to 1 year, the maximum value. You can read about the other options available in the Cache-Control header here: Cache-Control - HTTP | MDN
Now if we check that image again, it has the Cache-Control value that we set.