[EKS] [eks-pod-identity]: Support Pod Identity associations for existing running pods

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**Tell us about your request**
Support Pod Identity associations for existing running pods

**Which service(s) is this request for?**
EKS Pod Identity association

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Hi Team,

We're trying to use Pod Identity associations to integrate service accounts inside our K8s clusters to IAM roles. But it seems only pods created after the association will be able to use IAM roles. Previous running pods created before the association cannot use IAM role, even though they use the same service account.

We have multiple pods running our workload and we don't want to delete old pods and recreate new ones to be able to integrate with IAM roles.

So is there anyway to associate Pod Identity with running pods ?

No repository files, tests, or entry points are named. Start by investigating how EKS Pod Identity associations are applied to existing versus newly created pods, and define done as allowing already-running pods using the same service account to obtain the associated IAM role without deletion and recreation.

Written by the indexing model from the issue text.