OpenTelemetry exporter configuration. Resolved from config :hyper, Hyper.Cfg.Otel, proto:/endpoint:/headers: (config.exs), the [otel] toml table, then the standard OTEL_EXPORTER_OTLP_ENDPOINT env var. config/runtime.exs calls exporter_options/1 and feeds the result to config :opentelemetry_exporter.