Function span_layer 

pub fn span_layer<S>(
    service_name: impl Into<Value>,
    endpoint: &Url,
    protocol: OtlpProtocol,
) -> Result<OpenTelemetryLayer<S, SdkTracer>>
where
    for<'span> S: Subscriber + LookupSpan<'span>,

Creates a tracing [OpenTelemetryLayer] that exports spans to an OTLP endpoint.

This layer can be added to a [tracing_subscriber::Registry] to enable OpenTelemetry tracing with OTLP export to an url.