Enable Proxy Protocol

[mpstefan]

As a user of NGF
I want to enable proxy protocol for my application's endpoints
So that the client's IP address is preserved as the traffic is forwarded to my application.

Acceptance

• The user can enable proxy protocol for all Gateway listeners associated with the GatewayClass the NginxProxy parametersRef is attached to.
• When proxy protocol is enabled, gRPC and HTTP Routes will forward the client IP to the upstream service.
• API Reference documentation is updated to demonstrate how proxy protocol may be enabled.

### Tasks
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/2328
- [ ] Implement API

[github-actions]

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