Rework on setting AWS_REGION env variable

[runakash]

Set aws-region via kustomize edit command instead of the environment variable substitution. Environmental substitution was a bug documented as a feature, and is going to be fixed in the future release. Check this link for more context: kubernetes/website#35669

Also https://kubectl.docs.kubernetes.io/faq/kustomize/eschewedfeatures/#build-time-side-effects-from-cli-args-or-env-variables