[feat: aga] add accelerator model builder

[shraddhabang]

Issue

Fixes #1572

Description

This PR introduces the model builder for AWS Global Accelerator (AGA) resource

Core Model Builder Components:

• pkg/aga/model_build_accelerator.go - Accelerator model builder with support for:

  • Name generation and validation (63-character limit with sanitization)
  • IP address type configuration (IPv4/DualStack)
  • Static IP address assignment
  • Resource tagging with external managed tags validation

• pkg/model/aga/accelerator.go - Accelerator model definition

• pkg/aga/tag_helper.go - Tag management utilities for AGA resources

• Comprehensive unit testing

Testing

{"level":"info","ts":"2025-10-17T18:05:25Z","logger":"controllers.globalAccelerator","msg":"Reconciling GlobalAccelerator resources","name":"basic-accelerator","namespace":"shrabang-ns"}
{"level":"info","ts":"2025-10-17T18:05:25Z","logger":"controllers.globalAccelerator","msg":"successfully built model","model":"{\"id\":\"shrabang-ns/basic-accelerator\",\"resources\":{\"AWS::GlobalAccelerator::Accelerator\":{\"GlobalAccelerator\":{\"spec\":{\"name\":\"basic-test-accelerator\",\"ipAddresses\":[\"192.0.2.253\"],\"ipAddressType\":\"IPV4\",\"enabled\":true,\"tags\":{\"Environment\":\"test\",\"Team\":\"platform\",\"aga.k8s.aws/resource\":\"GlobalAccelerator\",\"aga.k8s.aws/stack\":\"shrabang-ns/basic-accelerator\",\"elbv2.k8s.aws/cluster\":\"gateway-api\"}}}}}}"}
{"level":"info","ts":"2025-10-17T18:05:25Z","logger":"controllers.globalAccelerator","msg":"Built model successfully","accelerator":"GlobalAccelerator","stackID":"shrabang-ns/basic-accelerator"}

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

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 🌟

[zac-nixon]

I don't think it's wise to re-use this as it's two different IaC systems

[zac-nixon]

Is this something we can generalize? This looks similar to the Gateway tag helper.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: shraddhabang, zac-nixon

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