Add Pod Service Account Annotation update option

[psolarcz]

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Adding option to specify list of annotation keys, for example: eks.amazonaws.com/role-arn - that will be appended with the cluster name. It will allow to use unique IAM Role per cluster.

To fix: https://github.com/zalando/postgres-operator/issues/2459

[Art3mK]

that would be really nice 👍 Not sure if appending cluster name is a good idea, I'd like to just pass role ARN via manifest to the SA.