[FLINK-34334][state] Add sub-task level RocksDB file count metrics

[hejufang]

What is the purpose of the change

Add sub-task level RocksDB file count metrics.

Brief change log

Get RocksDB file count of each level via RocksDB Property, and report it via Metrics reporter.

Verifying this change

Please make sure both new and modified tests in this PR follows the conventions defined in our code quality guide: https://flink.apache.org/contributing/code-style-and-quality-common.html#testing

This change is already covered by existing tests, such as org.apache.flink.contrib.streaming.state.RocksDBPropertyTest testRocksDBPropertiesValid.

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

• Dependencies (does it add or upgrade a dependency): 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: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? not documented

[flinkbot]

CI report:

• e9595e004b568678d4b3b92094a9b5cc8b1c38f6 Azure: SUCCESS

Bot commands

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[hejufang]

@flinkbot run azure

[hejufang]

@Zakelly kindly remind