What would you like to be added:
The ability to configure CORS policies on a HTTPRoute

Why this is needed:
CORS is needed to relax specific restrictions of SOP associated with requests sent from a web browser.

To learn more visit https://enable-cors.org/index.html

How some common data plane implementations that do this today

• Envoy - https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/cors_filter
• NGINX - https://enable-cors.org/server_nginx.html
• Many more in - https://enable-cors.org/server.html

Here is an example of existing high level APIs

• Contour - https://projectcontour.io/docs/v1.21.1/config/cors/
• Istio - https://istio.io/latest/docs/reference/config/networking/virtual-service/#CorsPolicy
• Envoy Gateway - https://gateway.envoyproxy.io/latest/user/cors/
• Ingress NGINX - https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/annotations/#enable-cors

Relates to envoyproxy/gateway#567