Migrate EBS CSI policy to AmazonEBSCSIDriverPolicy managed policy

[ConnorJC3]

Description

Today, eksctl applies an EBS CSI policy that is hardcoded inside of eksctl itself. This policy is out of date, in particular missing the change from kubernetes-sigs/aws-ebs-csi-driver#2190 which means that installations of the EBS CSI Driver from eksctl cannot create snapshots (without manually tweaking the policy).

Rather than continue to use a manual policy that must be kept in sync, this PR switches the EBS CSI policy over to the AWS-managed AmazonEBSCSIDriverPolicy (https://docs.aws.amazon.com/aws-managed-policy/latest/reference/AmazonEBSCSIDriverPolicy.html). Because this is an AWS-managed policy, this means any important policy changes will be synced by AWS and no manual change is needed in eksctl.

Checklist

• Added tests that cover your change (if possible) - Updated existing tests
• Added/modified documentation as required (such as the README.md, or the userdocs directory) - Don't think the docs need an update, but let me know if I missed something
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes
• (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟