Auto-populate OTLP resource attributes for metrics

[lbwexler]

Summary

• Auto-populates otlp.resourceAttributes on MetricsService from the same standard OTEL resource attributes that TraceService uses (service.name, service.instance.id, deployment.environment.name, service.version), ensuring metrics and traces arrive at the collector with consistent service identity.
• Extracts the four default resource attributes into an overridable getOtelResourceAttributes() method on ClusterConfig, so apps can customize values (e.g. mapping Development → dev to match platform conventions) before services initialize.
• Both TraceService and MetricsService now consume this shared source of truth via ClusterService.otelResourceAttributes.

Closes #536
Closes #537

Test plan

• Verify OTLP metrics export includes service.name, service.instance.id, deployment.environment.name, service.version resource attributes
• Verify OTLP traces continue to include the same resource attributes
• Verify overriding getOtelResourceAttributes() in an app's ClusterConfig subclass customizes both metrics and traces
• Verify existing otlpConfig settings (endpoint, timeout, headers) continue to work on both services

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