GCE: Fix lowercase value and alpha-missing annotation for ILB

[nicksardo]

What this PR does / why we need it:
Fixes #50426
Also explicitly sets an annotation as 'alpha'.

/assign @freehan @bowei

Release note:

GCE: Internal load balancer is enabled with annotation value "Internal" instead of "internal".

[freehan]

report a warning event?

[nicksardo]

This is just a helper function, so the best we could do is glog a warning. However, I haven't seen that for other deprecated annotations:

kubernetes/pkg/api/service/util.go

Lines 73 to 95 in e7b1814

	// RequestsOnlyLocalTraffic checks if service requests OnlyLocal traffic.
	func RequestsOnlyLocalTraffic(service *api.Service) bool {
	if service.Spec.Type != api.ServiceTypeLoadBalancer &&
	service.Spec.Type != api.ServiceTypeNodePort {
	return false
	}
	// First check the beta annotation and then the first class field. This is so that
	// existing Services continue to work till the user decides to transition to the
	// first class field.
	if l, ok := service.Annotations[api.BetaAnnotationExternalTraffic]; ok {
	switch l {
	case api.AnnotationValueExternalTrafficLocal:
	return true
	case api.AnnotationValueExternalTrafficGlobal:
	return false
	default:
	glog.Errorf("Invalid value for annotation %v: %v", api.BetaAnnotationExternalTraffic, l)
	return false
	}
	}
	return service.Spec.ExternalTrafficPolicy == api.ServiceExternalTrafficPolicyTypeLocal
	}

[freehan]

For generic k8s object fei/annotaion, I think we will throw errors during validation.

But since this is a GCP sepecific annotation, I am not sure how we expose it.

Log it at least.

[nicksardo]

Done

[freehan]

/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: freehan, nicksardo

Associated issue: 50426

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