fix: validate that fillInterval must not be '0s'

[MariamFahmy98]

Description

This PR adds a validation check to fillInterval so that it must not be set to '0s'.
Closes #11560

Change Type

/kind bug_fix

Changelog

None

Additional Notes

[timflannagan]

Thanks for taking a stab at this and fixing the other bug related to the local rate limit API. Had a question/comment about whether this proposed rule is sufficient to catch all the gwv1.Duration possible fields.

[timflannagan]

Would this catch other zero intervals being provided, e.g. "0h", "0m", etc? I'm looking at the

kgateway/internal/kgateway/extensions2/plugins/trafficpolicy/local_rate_limit_plugin.go

Lines 52 to 55 in ad0c830

	fillInterval, err := time.ParseDuration(string(t.TokenBucket.FillInterval))
	if err != nil {
	return nil, err
	}

and I think Envoy's local rate limit protobuf validation would still flag this configuration. See https://go.dev/play/p/E_k6jfT12BU for an easy reproducer.

I think the following rule could catch those edge cases:

+kubebuilder:validation:XValidation:rule="duration(self) > duration('0s')",message="fillInterval must not be '0s'"

We can validate by manually testing || adding a test case in the api_validation_test.go suite.

FYI @shashankram using gwv1.Duration as the underlying type instead of metav1.Duration.