feat: preserve metric suffixes in OpenMetrics 2.0

[arnabnandy7]

Summary

Add an OpenMetrics 2.0 naming option that preserves the suffix behavior of OpenMetrics 1.0 by default.

• Add io.prometheus.openmetrics2.suffixes.
• Default suffixes to true.
• Append missing unit suffixes and _total for counters.
• Avoid duplicating suffixes already present in metric names.
• Allow exact application-provided names with suffixes=false.
• Apply the selected naming behavior consistently to metadata and samples.
• Document the default and opt-out behavior.

Fixes #2518.

Why

Previously, enabling the OpenMetrics 2.0 writer exposed names exactly as passed to metric builders. For common instrumentation such as:

Counter.builder()
    .name("requests")
    .unit(Unit.BYTES)
    .build();

OpenMetrics 1.0 exposed requests_bytes_total, while OpenMetrics 2.0 exposed requests.

Changing the negotiated format could therefore create new series and silently break existing queries, alerts, recording rules, and dashboards.

With this change, the OpenMetrics 2.0 writer exposes requests_bytes_total by default. Users who need suffix-free or OpenTelemetry-style names can opt out:

io.prometheus.openmetrics2.suffixes=false

Implementation

The writer reuses MetricMetadata.expositionBaseName, which already contains the normalized unit suffix and preserves explicitly provided suffixes. Counter names then receive _total only when it is missing.

The existing OpenMetrics 1.0 summary-writing flow is reused with the selected metric name so summary metadata and samples follow the same configuration.

Validation

Ran targeted tests for the affected modules:

Tests run: 52, Failures: 0, Errors: 0, Skipped: 0
BUILD SUCCESS

Command:

./mvnw test \
  -pl prometheus-metrics-config,prometheus-metrics-exposition-textformats,prometheus-metrics-core \
  -am \
  -Dtest=OpenMetrics2PropertiesTest,PrometheusPropertiesTest,OpenMetrics2TextFormatWriterTest \
  -Dcoverage.skip=true \
  -Dsurefire.failIfNoSpecifiedTests=false

[zeitlinger]

Let's discuss the feature in #2518 first.

[github-actions]

⚠️ API changes detected — maintainer review required

This PR modifies the published API diff for the following module(s):

• prometheus-metrics-config

Please review the changes in docs/apidiffs/current_vs_latest/ carefully before approving.

[arnabnandy7]

Let's discuss the feature in #2518 first.

@zeitlinger sure thanks, I'll post in issue for further discussion.