[johnstonmatt]

Adds --enable-otel-metrics. With it, the main and event workers that --enable-otel instruments also export OpenTelemetry metrics, not only traces. Without it nothing changes.

The Edge Functions ingress needs this to push its availability counter to the regional OpenTelemetry collector (FUNC-1028). Today server.rs builds the workers' OtelConfig with tracing_enabled: true and leaves metrics_enabled at its default, so metrics.getMeter() in the main worker returns a no-op meter.

Verification

• cargo check -p cli and cargo fmt --check pass.
• The same vendored deno_telemetry code, run through stock Deno 2.9.8 with metrics on, pushed an @opentelemetry/api counter to an ADOT collector that wrote it to VictoriaMetrics.