feat: OTel tracing in LSD

Author: hinthornw

src/langsmith/env-var.mdx

@@ -24,6 +24,37 @@ A background run can execute for longer than 1 hour, but a client must reconnect
 
 Defaults to `3600`.
 
+## `OTEL_EXPORTER_OTLP_TRACES_ENDPOINT`
+
+Specify `OTEL_EXPORTER_OTLP_TRACES_ENDPOINT` to configure OpenTelemetry APM tracing for the deployment. Specify other [`OTEL_*` environment variables](https://opentelemetry.io/docs/collector/configuration/) to configure tracing, logging, and other instrumentation.
+
+```shell
+# If you set OTEL_EXPORTER_OTLP_TRACES_ENDPOINT or OTEL_EXPORTER_OTLP_ENDPOINT,
+# the server starts with OpenTelemetry instrumentation enabled.
+OTEL_EXPORTER_OTLP_TRACES_ENDPOINT=<target trace ingestion endpoint>
+OTEL_EXPORTER_OTLP_ENDPOINT=https://otlp.nr-data.net
+OTEL_SERVICE_NAME=MY_LANGSMITH_DEPLOYMENT
+OTEL_EXPORTER_OTLP_HEADERS=api-key=<YOUR_INGEST_LICENSE_KEY>
+# Common OTEL settings
+OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT=4095
+OTEL_EXPORTER_OTLP_COMPRESSION=gzip
+OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf
+OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE=delta
+# Optional: OTEL_PYTHON_LOGGING_AUTO_INSTRUMENTATION_ENABLED=true
+```
+
+For example, to submit OpenTelemetry traces to [New Relic's US region](https://docs.newrelic.com/docs/opentelemetry/best-practices/opentelemetry-otlp/), set the following:
+
+```shell
+OTEL_EXPORTER_OTLP_TRACES_ENDPOINT=https://otlp.nr-data.net/v1/traces
+OTEL_EXPORTER_OTLP_ENDPOINT=https://otlp.nr-data.net
+OTEL_EXPORTER_OTLP_HEADERS=api-key=<YOUR_INGEST_LICENSE_KEY>
+```
+
+<Note>
+OTel tracing was added in Agent Server version `0.5.32` and is currently in Alpha.
+</Note>
+
 ## `DD_API_KEY`
 
 Specify `DD_API_KEY` (your [Datadog API Key](https://docs.datadoghq.com/account_management/api-app-keys/)) to automatically enable Datadog tracing for the deployment. Specify other [`DD_*` environment variables](https://ddtrace.readthedocs.io/en/stable/configuration.html) to configure the tracing instrumentation.