Proxy Protocol configuration per user

This is an enhancement request for proxy protocol configuration in server. Allow configuring separate proxy network by user in addition to server-wide proxy network that is supported today.

From a security perspective, in addition to server-wide proxy-protocol-networks, it would be good to also optionally add a specific user-proxy-protocol-network column to user table. In which case, while the server accepts queries coming from any of the ip addresses specified in proxy-protocol-networks, the user can only be allowed to send queries through a specific Proxy as configured in its user table record. If the user-proxy-protocol-network column in user table is not configured for the specific user, then that user can accept query directly from any Proxy or without Proxy.