feat: Add OpenMetrics2 configuration support

[jaydeluca]

Part of #1912

[Copilot]

Pull request overview

Adds experimental OpenMetrics 2.0 configuration plumbing to the prometheus-metrics-config module so OM2 feature flags can be set via builder APIs and loaded from properties/env vars (as part of #1912).

Changes:

• Introduce OpenMetrics2Properties with OM2 feature-flag fields, builder, and property loading.
• Wire OM2 properties into PrometheusProperties and PrometheusPropertiesLoader.
• Add/extend unit tests covering defaults, builder usage, enable-all, and property loading/error handling.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusPropertiesLoader.java	Loads OpenMetrics2Properties and includes it in the assembled PrometheusProperties.
prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusProperties.java	Adds openMetrics2Properties field + getter and builder APIs (enableOpenMetrics2, direct assignment).
prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/OpenMetrics2Properties.java	New OM2 flag container with property parsing and builder (including enableAll()).
prometheus-metrics-config/src/test/java/io/prometheus/metrics/config/PrometheusPropertiesTest.java	Adds tests for OM2 builder patterns, defaults, and loading via PrometheusPropertiesLoader.
prometheus-metrics-config/src/test/java/io/prometheus/metrics/config/OpenMetrics2PropertiesTest.java	New tests for OM2 property loading, invalid values, builder behavior, and defaults.

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