chore(eks-v2-alpha): remove nested stack

[xazhao]

Reason for this change

In the current EKS module, kubectlProvider is created in a nested stack. The nested stack here is not necessary and hence moving it to the main stack.

Description of changes

Move kubectlProvider to the main stack.

Describe any new or updated permissions being added

<!— What new or updated IAM permissions are needed to support the changes being introduced ? -->

Description of how you validated changes

Updated unit tests so they all passed

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.95%. Comparing base (6c790fd) to head (da25112).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #32692   +/-   ##
=======================================
  Coverage   66.95%   66.95%           
=======================================
  Files         329      329           
  Lines       18662    18662           
  Branches     3257     3257           
=======================================
  Hits        12496    12496           
  Misses       5839     5839           
  Partials      327      327           

Flag	Coverage Δ
suite.unit	66.95% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	80.71% <ø> (ø)
packages/aws-cdk-lib/core	82.08% <ø> (ø)

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 12ecc13
• Result: SUCCEEDED
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