Add KMS key guidance for EKS on Outposts

[Daniel-Designs]

Documentation Update Request: KMS Key Configuration for EKS on Outposts

Current Documentation Gaps

1. Troubleshoot local Amazon EKS clusters on AWS Outposts lacks KMS key troubleshooting information
2. Deploy Amazon EKS on-premises with AWS Outposts doesn't cover KMS key considerations for EBS encryption

Proposed Changes

1. Add to Troubleshooting Guide

On "Cluster is stuck in CREATING state" cover this issue:

The control plane instances fail to create due to KMS key permissions for EBS volumes. When using customer-managed KMS keys for encrypted EBS volumes, the control plane instances will terminate if the key is not accessible. If the instances are terminated, either switch to an AWS managed KMS key or ensure your customer-managed key policy grants the necessary permissions to the cluster role.

2. Add to Deployment Guide

Add new section under prerequisites or considerations:

• KMS key requirements for EBS encryption
• Required permissions/policies for customer-managed keys

[pgasca]

Incorporated PR which handled point 1: #859