Inject `AWS_ZONE` environment variable into pods

**What would you like to be added**:
Can you please inject the AZ information as an environment variable at the pod level, it basically will be the same as the `AWS_REGION` one.

**Why is this needed**:
We are facing high complexity in deploying applications that require zone availability to run - for us it is elasticsearch, as we need to set that as an attribute on the pod level, and till now, it is not doable as you cannot set environment variable in a running pod and the pod doesn't have this information anywhere. there are many threads for the same request, it will be super nice and convenient to have this present as many applications are becoming AZ aware to achieve resilience over AWS.

The issue names no files, tests, or entry points; start by tracing how the webhook currently injects AWS_REGION into pod environments. Done means AWS_ZONE is also available at pod level with equivalent behavior, and the relevant tests pass.

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