Function to_grpc_insert_requests 

pub fn to_grpc_insert_requests(
    request: ExportMetricsServiceRequest,
    metric_ctx: &mut OtlpMetricCtx,
) -> Result<MetricsConversion>

Converts OpenTelemetry metrics without validating destination table schemas. Ingestion callers use prepare_metrics, run destination preflight, then call PreparedMetrics::finish to apply rejections and merge surviving points.

See https://github.com/open-telemetry/opentelemetry-proto/blob/main/opentelemetry/proto/metrics/v1/metrics.proto for data structure of OTLP metrics.