fix: correct deno opentelemetry exporter examples

[dvd233]

Summary

• document Deno's actual default OTLP HTTP/protobuf endpoint (localhost:4318)
• replace the unsupported OTEL_TRACES_EXPORTER=console example with Deno's built-in OTEL_EXPORTER_OTLP_PROTOCOL=console setting
• make the Jaeger example explicitly select OTLP gRPC for port 4317, and add a service name to the examples

Why

Fresh's OpenTelemetry page currently uses an exporter variable from other OpenTelemetry SDKs. Deno's built-in integration ignores that setting, so the advertised console command produces no telemetry. The page also sends the default HTTP/protobuf exporter to port 4317, which is the OTLP gRPC port; Deno's default HTTP/protobuf endpoint is localhost:4318.

The examples now match Deno's documented environment-variable names, protocol selection, and defaults. The Jaeger image line is intentionally left untouched because the separate open PR #3849 already updates that line; this change can merge cleanly with that work.

Tests

• direct Deno 2.9.6 A/B probe: OTEL_TRACES_EXPORTER=console emitted 0 spans/metrics; OTEL_EXPORTER_OTLP_PROTOCOL=console emitted 2 spans and 4 metrics
• direct OTLP wire probes: Deno's defaults sent HTTP/protobuf /v1/traces and /v1/metrics requests to localhost:4318; overriding only the endpoint to port 4317 still sent HTTP/protobuf, confirming the documented port/protocol mismatch
• deno task check:docs
• deno fmt --check docs/latest/advanced/opentelemetry.md
• deno task build-www
• three-way merge simulation with open PR docs: update Jaeger docker image from EOL v1 to current v2 #3849: clean
• git diff --check

Repository-wide deno task ok reaches the existing formatter gate but reports two pre-existing generated CSS formatting differences in www/static/prism.css and www/static/docsearch.css; neither file is changed by this PR.

Fixes #3834