Missing troubleshooting guide for common configuration and connectivity issues

[Vaishnav88sk]

Describe your use-case which is not covered by existing documentation.

When the plugin is misconfigured or the OTLP endpoint is unreachable, there is no single reference to help diagnose what went wrong. Users currently have to search through closed issues or guess at the cause.

Common scenarios with no documented fix:

• Builds complete but no traces appear in the backend
• Prometheus shows only a few metrics (queueSize, otlp_exporter_seen) instead of pipeline metrics
• ClassCircularityError thrown on install when Kubernetes plugin is also installed (ClassCircularityError thrown when installing the plugin #1201)
• Pipeline logs not forwarded to Elastic or Loki even after setting otel.logs.exporter=otlp
• Build agents silently failing to export because the OTLP endpoint is set to localhost
• Stage spans missing from traces for parallel pipeline branches

Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

• docs/setup-and-configuration.md - explains how to configure but not how to diagnose failures
• docs/build-logs.md - mentions agent reachability requirement but does not troubleshoot it
• ClassCircularityError thrown when installing the plugin #1201 - ClassCircularityError with no documented workaround
• opentelemetry-plugin >=2.2.1 won't work with opentelemetry-collector #380 - Prometheus missing metrics, caused by missing resource_to_telemetry_conversion config

Are you interested in contributing to the documentation?

Yes, I (@Vaishnav88sk) have already drafted the full content for docs/troubleshooting.md based on the existing docs, open issues, and the plugin source. I can submit a PR immediately once this issue is acknowledged.