How do I add MIME types?

Specifically, I need to serve `.wasm` files as application/wasm or WebAssembly.instantiateStreaming won't work. ring.util has [ext-mime-type](https://github.com/ring-clojure/ring/blob/master/ring-core/src/ring/util/mime_type.clj), but I can't figure out how to call it from boot-http.