Ingest NCCL Inspector OTLP/HTTP JSON (NCCL 2.31.2 NCCL_INSPECTOR_OTEL_EXPORT=1)

OTLP/HTTP JSON metrics receiver for the NCCL 2.31.2 Inspector OTel export (NCCL_INSPECTOR_OTEL_EXPORT=1, HTTP only) — or for an OpenTelemetry Collector otlphttp exporter with encoding: json in front of it. Body: ExportMetricsServiceRequest {resourceMetrics[].scopeMetrics[].metrics[]} with gauge/sum dataPoints and attributes; Content-Encoding: gzip is accepted. The same four metrics as /api/nccl/ingest-prometheus produce the same nccl_events rows (resource attribute host.name becomes the node when data points carry none). Protobuf bodies (application/x-protobuf) are rejected with 415 — set OTEL_EXPORTER_OTLP_PROTOCOL=http/json or put a Collector in between. Alias: POST /api/nccl/otlp/v1/metrics (so OTEL_EXPORTER_OTLP_ENDPOINT=<api>/api/nccl/otlp works with exporters that append the standard /v1/metrics path).