Add an Option to Log Proxied Client IPs

[thekief]

When using the Proxy Protocol, the ModSecurity module isn't currently able to access the client's IP. Thus, only the proxying server's IP is available.

For a project I work on, we needed an option to do so and implemented a patch we would like to upstream. Could I open a PR for it?

[airween]

Could I open a PR for it?

Sure, definitely.

This is the best place to discuss every modification.