Support for Private Network Access in CORS plugin

[mrjoops]

Hi all!

With the recent release of Chrome 102, Google rolled out a new CORS policy preventing public websites to access private networks (look at this blog post for details: https://developer.chrome.com/blog/private-network-access-preflight/).

The fact is that my development team already encountered an issue on our VPN-protected testing infrastructure, running on Kong with the CORS plugin : the "private" status of our network is set to "unknown" by Chrome, so it falls back to the "private" status.

We mitigated the problem using the response transformer plugin but since it's about the Access-Control-Allow-Private-Network header, it makes sense to add support for it in the CORS plugin with a boolean property named "config.private" or "config.private_network".

Thank you in advance for considering this suggestion!