Prometheus/OpenTelemetry Native Export

Currently, FoundationDB exposes metrics via its JSON status output `(fdbcli --exec "status json")`. To integrate with modern observability platforms like Prometheus, Grafana, or Datadog, users must:

- Periodically scrape the JSON status endpoint
- Parse the complex nested JSON structure
- Transform metrics into Prometheus format (labels, counters, gauges)
- Run a separate exporter sidecar process

This creates operational overhead, potential data inconsistency, and monitoring gaps between scrapes.

Start by reviewing the existing `fdbcli --exec "status json"` metrics output and how its nested values are exposed. Define the native Prometheus/OpenTelemetry export surface and metric mapping before implementation. Done means users can consume metrics directly without periodically parsing JSON or running a separate exporter sidecar.

Written by the indexing model from the issue text.