Implement gep-3388 (Retry Budget)

[zirain]

xref: kubernetes-sigs/gateway-api#3488

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[arkodg]

hey @zirain would like to hold off on this until we've built broader consensus on if/when/how we'll support X APIs.
these are experimental APIs that may break, and as an implementation we may not be able to control when this happens, yet we'll need to keep upgrading Gateway API versions to access the stable features.

my first thought, is to make support for X APIs opt/in using the extensionAPIs field in EnvoyGateway, which also controls the CRDs installed via helm

cc @envoyproxy/gateway-maintainers @envoyproxy/gateway-reviewers

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