Add configurable OpenTelemetry sampler for OTLP tracing

[Shamly-Shanawaz]

Description

This PR improves OpenTelemetry OTLP tracing by making the trace sampler configurable via deployment.toml (remote_tracer.sampler_mode).

Issue

wso2/api-manager#5075

[wso2-engineering]

AI Agent Log Improvement Checklist

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#### Log Improvement Suggestion No: 1
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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

Plan: Pro

Run ID: 0cde1bd4-39d3-42c2-b55b-eb524d2eb821

📥 Commits

Reviewing files that changed from the base of the PR and between 56a4da8 and 1b32f67.

📒 Files selected for processing (3)

• components/apimgt/org.wso2.carbon.apimgt.tracing/src/main/java/org/wso2/carbon/apimgt/tracing/telemetry/OTLPTelemetry.java
• components/apimgt/org.wso2.carbon.apimgt.tracing/src/main/java/org/wso2/carbon/apimgt/tracing/telemetry/TelemetryConstants.java
• features/apimgt/org.wso2.carbon.apimgt.core.feature/src/main/resources/conf_templates/templates/repository/conf/api-manager.xml.j2

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📝 Walkthrough

Walkthrough

Adds configurable trace sampling to the OTLP telemetry implementation. TelemetryConstants gains four sampler-related string constants. OTLPTelemetry adds a getConfiguredSampler() method that maps the configured SamplerMode value to an OpenTelemetry Sampler, with fallback and warning logging, and wires it into SdkTracerProvider. The api-manager.xml.j2 template conditionally emits a SamplerMode XML element when the property is set.

Changes

Configurable OTLP Sampler

Layer / File(s)	Summary
Sampler constants and OTLPTelemetry resolver ...tracing/telemetry/TelemetryConstants.java, ...tracing/telemetry/OTLPTelemetry.java	TelemetryConstants adds OTLP_CONFIG_SAMPLER, SAMPLER_ALWAYS_ON, SAMPLER_ALWAYS_OFF, and SAMPLER_PARENT_BASED. OTLPTelemetry adds getConfiguredSampler() mapping those values to Sampler.alwaysOn, Sampler.alwaysOff, or Sampler.parentBased(alwaysOn) with warning-and-fallback for unknown values, and applies it via .setSampler() on the SdkTracerProvider builder.
SamplerMode config template features/apimgt/.../conf_templates/templates/repository/conf/api-manager.xml.j2	Adds a Jinja {% if %} block under OpenTelemetry/RemoteTracer to conditionally emit <SamplerMode> from apim.open_telemetry.remote_tracer.sampler_mode.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: adding configurable OpenTelemetry sampler support for OTLP tracing, which is the primary objective of the changeset.
Description check	✅ Passed	The description is directly related to the changeset, explaining that the PR makes the trace sampler configurable via deployment.toml and references the corresponding issue.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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