Beta — may change; breaking changes are coordinated with affected
customers. Suitable for evaluation, not production reliance.

Lists environments and the service namespaces with active telemetry in
the [startTime, endTime) window. environment is an optional
exact-match filter (omit to return all environments). This endpoint
does not bucket metrics, so it accepts only startTime/endTime (no
series bucketing) and returns no redMetrics and no related.

Each row's serviceNamespaces is the set observed for that environment,
capped at a server limit; when the full set exceeds the cap, the array
is truncated and truncated is true. The list is never paged separately
— pagination is on the environments axis. Services emitting no
service.namespace contribute nothing; the array never contains null.