[Docs] Update IRSA doc when pod-identity-webhook PR is merged

Currently the doc for IRSA points to an older commit of the pod-identity-webhook in its in-cluster installation step (https://github.com/aws/eks-anywhere/blob/main/docs/content/en/docs/reference/clusterspec/irsa.md#deploy-pod-identity-webhook)
This is because the latest commit of pod-identity-webhook does not work for in-cluster installation because of a recent change in the pod-identity-webhook repo. This PR fixes it: https://github.com/aws/amazon-eks-pod-identity-webhook/pull/150
Once this PR is merged, we can update the docs to point to the latest commit. If needed also update the image tag

Read docs/content/en/docs/reference/clusterspec/irsa.md at the “Deploy pod identity webhook” section, then check whether aws/amazon-eks-pod-identity-webhook#150 is merged. Done means updating the referenced commit, and the image tag if needed, to the current working version.

Written by the indexing model from the issue text.