Send traces (OTLP/HTTP)

The OTLP/HTTP trace endpoint: point an OpenTelemetry OTLPSpanExporter here with a Voxli API key as Authorization: Bearer <key>. Takes an ExportTraceServiceRequest as protobuf or JSON, optionally gzip or deflate compressed. Each span belongs to the conversation named by its gen_ai.conversation.id or session.id attribute (or one on another span of its trace, or on its resource). A span that names none yet is held until a span of its trace does. Spans are stored as received and merged per conversation in the background.