Feature Request: Add Proxy Protocol Configuration Support to APISIX Helm Chart

I would like to add support for configuring the PROXY protocol in the APISIX helm chart. Currently, the PROXY protocol configuration exists in the template as commented code, but there's no way to enable or configure it via values.yaml.

Motivation

The PROXY protocol allows load balancers to pass client connection information to APISIX. This is especially useful in Kubernetes environments where APISIX is deployed behind a load balancer, and the original client IP needs to be preserved.

Implementation Plan

- [ ] Added proxy protocol configuration options to values.yaml with default values:
proxyProtocol:
enabled: false
listenHTTPPort: 9181
listenHTTPSPort: 9182
enableTCPPP: false
enableTCPPPToUpstream: false
- [ ] Updated configmap.yaml to conditionally include proxy_protocol configuration when enabled
- [ ] Added schema validation in values.schema.json for the new options
- [ ] Updated README.md with documentation for the new configuration options

These changes allow users to easily enable and configure proxy protocol support through the helm chart values, rather than having to manually modify the configmap.

Start with the commented PROXY protocol configuration in configmap.yaml, then inspect values.yaml, values.schema.json, and README.md. Add the listed options with their defaults, conditionally expose the configuration when enabled, validate the values, and document the settings; done means all four files support the same configuration without manual ConfigMap edits.

Written by the indexing model from the issue text.