Kubernetes event handling exhibits inconsistent behaviour when multiple sync providers are configured

[skyerus]

While expanding the e2e test suite to cover #319 I discovered that configuring multiple sync providers causes unexpected behaviour in the kubernetes event listener. flagd's internal state is not being updated to reflect a change in the FeatureFlagConfiguration.
To reproduce this:

1. Check out the branch in my PR.
2. Deploy the operator.
3. Run kubectl -n open-feature-operator-system apply -f ./test/e2e/e2e.yml
4. Expose the service kubectl -n open-feature-operator-system port-forward service/open-feature-e2e-test-service 30000:30000
5. Run the test (passes/fails intermittently) ./test/e2e/tests/002.crd-configuration-reconciliation.sh

Tailing flagd's logs I can see that the event is received, the problem lies somewhere within https://github.com/open-feature/flagd/blob/main/pkg/sync/kubernetes/kubernetes_sync.go#L225

[toddbaert]

I think this was resolved with both these PRs:

#326

open-feature/flagd#339

(but we still need #325 for tests)