feat: re-enable proxy-protocol configuration nodes

[heresie]

Hello everybody 👋🏻

I contributed in june 2023 to this project by adding configuration nodes in helm chart allowing clean proxy-protocol configuration (#528).

Recently we wanted to upgrade our current APISIX release because of CVE-2024-32638 but during upgrade we noticed that all proxy-protocol configuration nodes have disapeared since this PR : #738

Currently, we are unable to upgrade APISIX without manually editing ConfigMaps to re-enable proxy-protocol, and that's a big problem because we cannot automatize our deployments. I think we are not alone in this case (for example @adussarps in #748).

Can you consider my PR that re-introduce needed changes ?

Here are example values for testing purpose :

global:
  enableIPv6: false
  storageClass: <my-storage-class>

apisix:
  kind: DaemonSet
  ssl:
    enabled: true
  proxyProtocol:
    enabled: true
    listenHttpPort: 9181
    listenHttpsPort: 9182

service:
  type: NodePort
  http:
    enabled: true
  proxyProtocol:
    http:
      enabled: true
      nodePort: 30080
      containerPort: 9181
    https:
      enabled: true
      nodePort: 30443
      containerPort: 9182

This PR also bumps Chart Version to the next minor : 2.8.0.

All comments are welcome.