Span events and annotations

tracing-opentelemetry records every tracing event inside a span as an event of that span. Neither exporter sends them by default. They would be reported twice, once with the span in Trace Explorer and once as a log entry by the logging layer.

• The OTLP exporter leaves them off the spans. with_span_events(true) on GcpOtlpExporterBuilder, before create_provider() or span_exporter(), sends them with the span.
• The Cloud Trace API exporter does not export them. with_span_events(true) on GcpCloudTraceExporterBuilder, before create_provider(), exports them as annotations (time_events).

Span status, links and attributes are exported either way.

Events added through the OpenTelemetry API with span.add_event(...) are span events too, and follow the same rule. Whether to log an event or attach it to a span is a choice of where it is read: a log entry is searched in Logging and linked to its trace, an annotation is shown on the span in Trace Explorer.