fix(cloudwatch): unrecognized statistic warning when using percentileRank statistic in Stats helper

[xazhao]

Issue # (if applicable)

Closes #29465.

Reason for this change

There shouldn't be a warning when Stats.percentileRank

Description of changes

Add a new parser for percentileRank statistic

Description of how you validated changes

unit test

Checklist

• 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

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[xazhao]

The PR just removes the warning so no integration test is required.

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

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[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 52e5b1e
• Result: SUCCEEDED
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[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).