[FEATURE] Added support for automountServiceAccountToken

[KaijiroHyodo]

Is your feature request related to a problem?

I am using GKE Autopilot to deploy OpenSearch via OpenSearch-Operator and Statefulset automountServiceAccountToken option is already implemented in OpenSearch but no option in OpenSearch-Operator to set this functionality.
opensearch-project/helm-charts#425

Because of that need to download JSON key file from service account and save in keystore.

What solution would you like?

Add new option inside of nodePool to be able to set automountServiceAccountToken true or false

[dblock]

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