Fixes for K8s 1.27 and Flux 2.1.2

[ivallhon]

Issue #, if available: https://github.com/aws-samples/flux-eks-gitops-config-tenant/issues/1

Description of changes: In recent versions of Flux, the beta APIs are deprecated, and the validation property is not part of the schema of kustomize.toolkit.fluxcd.io/v1, so the podinfo-team Kustomization fails to be created. Also, flagger version 1.21.0 fails to create the podinfo canary on K8s 1.27 (default K8s version created by eksctl). Updated version to 1.34.0.

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