docs: promote OTEL console exporter to a dedicated section (2.8)

runtime/fundamentals/open_telemetry.md

@@ -92,6 +92,41 @@ You can also create your own metrics, traces, and logs using the
 `npm:@opentelemetry/api` package.
 [Learn more about user defined metrics](#user-metrics).
 
+## Console exporter
+
+For local development and writing instrumentation, set
+`OTEL_EXPORTER_OTLP_PROTOCOL=console` to make Deno write spans, logs, and
+metrics directly to stderr in a human-readable text format. No OTLP collector
+is needed and no endpoint configuration is required.
+
+```sh
+OTEL_DENO=true OTEL_EXPORTER_OTLP_PROTOCOL=console deno run my_script.ts
+```
+
+Example output:
+
+```
+SPAN inner span [00000000000000000000000000000001/0000000000000002] Internal 0.495ms
+  parent: 0000000000000001
+  scope: example-tracer
+  key: value
+LOG [INFO] 2026-03-14T13:47:07.235Z "hello from inner"
+  scope: deno@2.8.0
+  trace: 00000000000000000000000000000001/0000000000000002
+METRIC http.server.request.duration histogram
+  count: 3 sum: 0.012s
+```
+
+The console exporter is the recommended way to:
+
+- iterate on custom traces / metrics without round-tripping through a
+  collector,
+- verify that auto-instrumentation is firing as expected, and
+- include OTel output in CI logs for ad-hoc debugging.
+
+For production, switch to `http/protobuf`, `http/json`, or `grpc` — see
+[Configuration](#configuration).
+
 ## Auto instrumentation
 
 Deno automatically collects and exports some observability data to the OTLP