This commit adds CORS support for Private Network Access
by adding an Access-Control-Allow-Private-Network response
header when the preflight request is sent with an
Access-Control-Request-Private-Network header and that
Private Network Access has been enabled in the CORS
configuration.
See https://developer.chrome.com/blog/private-network-access-preflight/
for more details.
Closes gh-31974
(cherry picked from commit 318d460256)