feat(ecs): add scaleInAfter support to ManagedInstancesCapacityProvider

[jasdeepbhalla]

Issue # (if applicable)

Closes #36119

Reason for this change

AWS recently introduced configurable scale-in delay for ECS Managed Instances via the InfrastructureOptimization.ScaleInAfter property.

This capability is currently available in CloudFormation but is not exposed in the CDK L2 construct ManagedInstancesCapacityProvider.

Exposing this option allows CDK users to:

• Control how long ECS waits before optimizing idle or underutilized EC2 instances
• Reduce unnecessary instance churn
• Adopt the latest ECS Managed Instances features without using escape hatches

Description of changes

This PR adds native L2 support for configuring the ECS Managed Instances scale-in delay:

• Added a new optional property: scaleInAfter?: Duration to ManagedInstancesCapacityProviderProps
• When specified, the construct now synthesizes:

ManagedInstancesProvider:
  InfrastructureOptimization:
    ScaleInAfter: <seconds>

• The property is only emitted when explicitly provided, preserving default ECS behavior
• Added validation to ensure the value is within AWS-supported limits (0–3600 seconds)
• This change is backward-compatible and does not alter existing behavior unless the new property is used.

Describe any new or updated permissions being added

None

Description of how you validated changes

• Added Unit and Integration tests for this change

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

[aws-cdk-automation]

(This review is outdated)

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
Please try merge from main to avoid findings unrelated to the PR.

---

	Tests	Passed ✅	Skipped	Failed
Security Guardian Results	50 ran	50 passed

Test	Result
No test annotations available

• View Security Guardian Results

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
Please try merge from main to avoid findings unrelated to the PR.

---

	Tests	Passed ✅	Skipped	Failed
Security Guardian Results with resolved templates	50 ran	50 passed

Test	Result
No test annotations available

• View Security Guardian Results with resolved templates