[FLINK-38704][runtime] Convert config values to String

[mukul-8]

What is the purpose of the change

Fixes the Prometheus metrics reporter (and potentially other reporters) not loading configured port values.

The issue occurs because numeric YAML configuration values are stored as Integer/Long objects, but Properties.getProperty() only returns Strings. When MetricConfig.getString() is called for numeric values like metrics.reporter.prom.port, it returns null, causing reporters to fall back to default values.

Note: The bug only reproduces when a single number is assigned to the port (e.g., 9999). It works correctly when a port-range is used (e.g., 9000-9100) because ranges are stored as Strings.

Safety: This change is safe and non-breaking. Properties are inherently String-based (all values are stored and retrieved as Strings), so converting values to String at insertion time maintains the expected behavior while fixing the type mismatch issue.

Workaround: Quote the port value in YAML configuration: metrics.reporter.prom.port: "9999"

Brief change log

• Modified addAllToProperties method to convert all configuration values to String before adding to Properties

Verifying this change

This change fixes the bug where:

• Configuration loads: metrics.reporter.prom.port=9999
• But reporter starts on default port 9249 instead

After the fix, the configured port is correctly applied.

Added test case to verify this change is working fine.

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? no
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[flinkbot]

CI report:

• b55f194 Azure: FAILURE

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[davidradl]

can the entry.getValue() ever be null? Maybe add a test for this case.

[mukul-8]

Good catch. I've verified that entry.getValue() cannot be null. The Configuration.setValueInternal() method ensures only non-null values are stored in the internal map, so entry.getValue() will always return a non-null object at this point.

[mukul-8]

I've identified an issue with the current implementation. The .toString() conversion affects complex types like HashMap, which produces non-deterministic string representations due to unordered iteration. This causes the PythonDependencyUtilsTest.testPythonFiles test to fail in CI (though it passed locally due to the non-deterministic nature).

I'll update the implementation to only convert primitive types (Number, Boolean) to String while preserving the original behavior for complex types. This will fix the metrics reporter bug without breaking existing functionality.