support GEP-1731 Configurable Retries

[zirain]

kubernetes-sigs/gateway-api#3199

wait for gateway api v1.2

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 30 days.

[zirain]

@guydc @arkodg what is the relationship between https://gateway.envoyproxy.io/docs/api/extension_types/#retry and gep-1731?

[arkodg]

its similar to timeouts, we'll have to support both (core gateway API as well as the extension field in BackendTrafficPolicy), but core setting overrides extension setting