Description:
Introduce a hierarchical policy attachment called TrafficPolicy that can be applied to the Gateway and HTTPRoute / xRoute resources to further configure the traffic ingressing in which can be applied either for the downstream connection or upstream connection.

kind: TrafficPolicy
spec:
  default:
    downstream:
      keepalive: .....
    upstream:
      keepalive: .....
      cors:
      loadBalancer:
      tls:
  targetRef:
    kind: Gateway
    name: example

Relates to

• proposal: LoadbalancingPolicy #1105
• KeepAlive support #1031
• Support Route timeout And Cluster connect timeout configure #877
• support upstream tls #837
• Support Authentication Overrides and Defaults #731
• Enabling CORS for a HTTPRoute  #567
• Add Support for WAF #671
• Introduce a CRD for backend details #492
• Support downstream and upstream Proxy Protocol #1328