[FLINK-31769] feat: quantile to aggregated metrcis

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What is the purpose of the change

This PR adds quantiles for the aggregated metrics. Using this metrics we can use quantile for the autoscaler.

I will send follow-up PR if this change is approved.

Brief change log

• Quantile metrics can be retrieve by explicit REST API request.

Verifying this change

Please make sure both new and modified tests in this PR follow the conventions for tests defined in our code quality guide.

This change added tests and can be verified as follows:

• Added test that retrieve valid quantiles.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): yes / no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? docs

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-By: Claude Opus 4.8 (1M context)

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CI report:

• Unknown: CANCELED
• 514d18b Azure: PENDING

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