feat: respond to preflight requests

[notnmeyer]

respond to preflight OPTIONS requests,

➜ curl -i -X OPTIONS http://localhost:8080
HTTP/1.1 204 No Content
Access-Control-Allow-Headers: *
Access-Control-Allow-Methods: *
Access-Control-Allow-Origin: *
Access-Control-Max-Age: 86400
Connection: keep-alive
Date: Mon, 08 Jan 2024 17:54:14 GMT