/metrics/track ignores the limit query parameter

[gmarzot]

limit has no effect; the endpoint always uses admin.track_metrics_endpoint_default_limit.

$ curl -s 'localhost:8000/metrics/track?limit=1000'
matched 17 tracks, exceeds limit=10; narrow the namespace or raise limit

$ curl -s 'localhost:8000/metrics/track?limit=50'
matched 17 tracks, exceeds limit=10; narrow the namespace or raise limit

docs/metrics.md documents it as accepted and clamped to track_metrics_endpoint_max_limit (1000), and the error message tells the caller to raise a limit that raising does not change.

Namespace scoping works, so per-namespace scrapes are unaffected (#539 relies on that). It blocks the documented escape hatch for a namespace holding more tracks than the default.

Seen on v0.2.1-48-g3ba4740e.