feat(eks): support CUSTOM amiType

[Artemigos]

Issue # (if applicable)

Closes #30641.

Reason for this change

Node groups with custom AMI are supported by CloudFormation, but not by CDK. This adds that support.

Description of changes

• added CUSTOM to the NodegroupAmiType enum
• always add CUSTOM to possibleAmiTypes when validating instanceTypes CPU architecture against amiType
• verify that launchTemplateSpec is defined when using CUSTOM

Description of how you validated changes

Added unit tests checking valid deployment as well as failure when CUSTOM is used, but launchTemplateSpec isn't defined.

Checklist

• [x] 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

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 432ead4c4c5786a379005f5bd08f0ee8d5b2d58d
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[aws-cdk-automation]

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[aws-cdk-automation]

This PR has been deemed to be abandoned, and will be automatically closed. Please create a new PR for these changes if you think this decision has been made in error.

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