[Enhancement] aws_eks_addon: Support configuring namespace

[phuhung273]

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

Description

EKS Addon support configuring namespace

Relations

Closes #44086

References

https://aws.amazon.com/about-aws/whats-new/2025/08/amazon-eks-namespace-configuration-addons/

Output from Acceptance Testing

% make testacc TESTS=TestAccEKSAddon_namespace PKG=eks
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.24.6 test ./internal/service/eks/... -v -count 1 -parallel 20 -run='TestAccEKSAddon_namespace'  -timeout 360m -vet=off
2025/08/29 22:08:48 Creating Terraform AWS Provider (SDKv2-style)...
2025/08/29 22:08:48 Initializing Terraform AWS Provider (SDKv2-style)...
=== RUN   TestAccEKSAddon_namespace
=== PAUSE TestAccEKSAddon_namespace
=== CONT  TestAccEKSAddon_namespace
--- PASS: TestAccEKSAddon_namespace (515.28s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/eks        515.500s
...

[github-actions]

✅ Thank you for correcting the previously detected issues! The maintainers appreciate your efforts to make the review process as smooth as possible.

[github-actions]

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