docs(eks): clarify TaintEffect enum usage for AWS vs Kubernetes contexts

[pahud]

Issue # (if applicable)

Related to #34780

Reason for this change

After thorough investigation, the original issue was caused by a misunderstanding of taint effect format differences between AWS EKS API and Kubernetes manifests. The TaintEffect enum is working correctly as designed for its intended purpose (EKS NodeGroups).

Description of changes

Documentation Changes:

• Added comprehensive documentation to the TaintEffect enum explaining the format differences between AWS EKS API and Kubernetes manifests
• Clarified that the enum is specifically designed for EKS NodeGroups (AWS API format)
• Provided guidance on when to use the enum vs string literals

Key findings from investigation:

• AWS EKS API expects: NO_SCHEDULE, PREFER_NO_SCHEDULE, NO_EXECUTE
• Kubernetes manifests expect: NoSchedule, PreferNoSchedule, NoExecute
• This difference is documented in the AWS EKS User Guide
• Integration tests confirmed that changing enum values breaks EKS NodeGroup deployments

Why the original approach was incorrect:
The TaintEffect enum cannot be changed because it would break all existing EKS NodeGroup deployments. The enum is correctly designed for AWS EKS API, not for direct Kubernetes manifests.

Correct solution for users:

• Use TaintEffect enum for EKS NodeGroups (AWS API format)
• Use string literals with PascalCase for Kubernetes manifests (Kubernetes format)

Describe any new or updated permissions being added

No new or updated IAM permissions are needed for this change.

Description of how you validated changes

• Integration Testing: Confirmed that attempting to change enum values causes EKS API validation failures
• AWS Documentation Review: Verified the format differences in official AWS documentation
• Code Analysis: Confirmed that the enum is used correctly throughout the codebase for EKS NodeGroups

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

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[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: c17396c
• Result: FAILED
• Build Logs (available for 30 days)

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[Abogical]

There is a lint failure. See logs [here](Build Logs).

@aws-cdk/aws-eks-v2-alpha: /codebuild/output/src1131233384/src/github.com/aws/aws-cdk/packages/@aws-cdk/aws-eks-v2-alpha/lib/managed-nodegroup.ts
@aws-cdk/aws-eks-v2-alpha:   159:3   error  Trailing spaces not allowed  no-trailing-spaces
@aws-cdk/aws-eks-v2-alpha:   163:3   error  Trailing spaces not allowed  no-trailing-spaces
@aws-cdk/aws-eks-v2-alpha:   166:66  error  Trailing spaces not allowed  no-trailing-spaces
@aws-cdk/aws-eks-v2-alpha:   168:3   error  Trailing spaces not allowed  no-trailing-spaces

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Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

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