feat: improve telemetry (#2590)

# What does this PR do?

* Use a single env variable to setup OTEL endpoint
* Update telemetry provider doc
* Update general telemetry doc with the metric with generate
* Left a script to setup telemetry for testing

Closes: https://github.com/meta-llama/llama-stack/issues/783

Note to reviewer: the `setup_telemetry.sh` script was useful for me, it
was nicely generated by AI, if we don't want it in the repo, and I can
delete it, and I would understand.

Signed-off-by: Sébastien Han <seb@redhat.com>

llama_stack/providers/inline/telemetry/meta_reference/telemetry.py

@@ -86,24 +86,27 @@ class TelemetryAdapter(TelemetryDatasetMixin, Telemetry):
             provider = TracerProvider(resource=resource)
             trace.set_tracer_provider(provider)
             _TRACER_PROVIDER = provider
-            if TelemetrySink.OTEL_TRACE in self.config.sinks:
-                if self.config.otel_trace_endpoint is None:
-                    raise ValueError("otel_trace_endpoint is required when OTEL_TRACE is enabled")
-                span_exporter = OTLPSpanExporter(
-                    endpoint=self.config.otel_trace_endpoint,
-                )
-                span_processor = BatchSpanProcessor(span_exporter)
-                trace.get_tracer_provider().add_span_processor(span_processor)
-            if TelemetrySink.OTEL_METRIC in self.config.sinks:
-                if self.config.otel_metric_endpoint is None:
-                    raise ValueError("otel_metric_endpoint is required when OTEL_METRIC is enabled")
-                metric_reader = PeriodicExportingMetricReader(
-                    OTLPMetricExporter(
-                        endpoint=self.config.otel_metric_endpoint,
+
+            # Use single OTLP endpoint for all telemetry signals
+            if TelemetrySink.OTEL_TRACE in self.config.sinks or TelemetrySink.OTEL_METRIC in self.config.sinks:
+                if self.config.otel_exporter_otlp_endpoint is None:
+                    raise ValueError(
+                        "otel_exporter_otlp_endpoint is required when OTEL_TRACE or OTEL_METRIC is enabled"
                     )
-                )
-                metric_provider = MeterProvider(resource=resource, metric_readers=[metric_reader])
-                metrics.set_meter_provider(metric_provider)
+
+                # Let OpenTelemetry SDK handle endpoint construction automatically
+                # The SDK will read OTEL_EXPORTER_OTLP_ENDPOINT and construct appropriate URLs
+                # https://opentelemetry.io/docs/languages/sdk-configuration/otlp-exporter
+                if TelemetrySink.OTEL_TRACE in self.config.sinks:
+                    span_exporter = OTLPSpanExporter()
+                    span_processor = BatchSpanProcessor(span_exporter)
+                    trace.get_tracer_provider().add_span_processor(span_processor)
+
+                if TelemetrySink.OTEL_METRIC in self.config.sinks:
+                    metric_reader = PeriodicExportingMetricReader(OTLPMetricExporter())
+                    metric_provider = MeterProvider(resource=resource, metric_readers=[metric_reader])
+                    metrics.set_meter_provider(metric_provider)
+
             if TelemetrySink.SQLITE in self.config.sinks:
                 trace.get_tracer_provider().add_span_processor(SQLiteSpanProcessor(self.config.sqlite_db_path))
             if TelemetrySink.CONSOLE in self.config.sinks: