✨ eks: skip aws:-prefixed tags in nodegroup reconciliation

[cPu1]

What type of PR is this?

/kind feature

What this PR does / why we need it:

When reconciling tags for EKS managed nodegroups and Fargate profiles, ignore aws:-prefixed keys when building the list of keys to remove, using the same reserved-prefix logic as pkg/cloud/tags for tag application.

Those tags are not part of CAPA’s desired tag map since the validating webhooks forbid them in additionalTags, but they can exist on nodegroups created outside of CAPA (e.g., via CloudFormation). Including them in UntagResource triggers an API validation error, failing reconciliation and adoption of pre-existing nodegroups.

Additionally, this changelist also replaces manual copying of variables (kCopy/vCopy) with ptr.To() so the loop-variable aliasing workaround is not required.

This has been tested on an eksctl-provisioned cluster which creates nodegroups using CloudFormation. The AWS-reserved tags on the nodegroup (aws:cloudformation:stack-name, aws:cloudformation:logical-id and aws:cloudformation:stack-id) were correctly skipped and reconciliation passed.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #5964

Special notes for your reviewer:

Checklist:

• squashed commits
• includes documentation
• includes AI generated content
• includes emoji in title
• adds unit tests
• adds or updates e2e tests

Release note:

EKS: Skip aws:-prefixed tag keys when reconciling managed nodegroup and Fargate profile tags so `UntagResource` is not called for AWS-reserved keys.

[k8s-ci-robot]

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @cPu1. Thanks for your PR.

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[nrb]

/ok-to-test

[cPu1]

@nrb tests are passing. Can you review this PR?