docs: updating documentation on how to setup IRSA on AWS

[domderen]

I tried configuring my Argo-Server to use s3 as an artifact repository, and then archive all logs automatically, and it worked fine. But then when I wanted to load those logs in the Argo-Server UI using the link https://<arg_server_host>/artifacts/argo/<workflow_name>/<pod_name>/main-logs I got the following error:

failed to create new S3 client: WebIdentityErr: failed fetching WebIdentity token: 
caused by: WebIdentityErr: unable to read file at /var/run/secrets/eks.amazonaws.com/serviceaccount/token
caused by: open /var/run/secrets/eks.amazonaws.com/serviceaccount/token: permission denied

Reading through similar issues here: kubernetes-sigs/external-dns#1185 I found out that IRSA requires this setting on the Deployment:
spec.template.spec.securityContext.fsGroup: 65534 to fix the above issue.

I thought it would be helpful to others to find information how to deal with it here, rather than search for the answers if they hit this problem.

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