obs: migrate cloud OTel collectors to Prometheus native histograms

**Summary**

Once CockroachDB's metrics emit Prometheus native histograms (the goodhistogram migration; CRDB already supports native-histogram export via `COCKROACH_ENABLE_PROMETHEUS_NATIVE_HISTOGRAMS`, which represents a histogram as a single exponential time series rather than a collection of per-bucket counter series), the cloud OpenTelemetry collectors that scrape and forward CRDB metrics should ingest the native form to realize the benefit — far fewer series and better resolution.

This is a verify-then-migrate item: the collector configuration lives in the managed-service / infra repos, not in `cockroach`, so the current behavior needs to be checked first.

**Tasks**
- [ ] Confirm whether the cloud OTel collectors already ingest CockroachDB native histograms after the migration (vs. classic per-bucket series). If so, close this.
- [ ] If not, enable native-histogram scraping/forwarding in the collector config and verify downstream storage and dashboards handle the native format.

Epic CRDB-63921

Jira issue: CRDB-64882