How to: Management API
Optional, can be turned on with `--mgmt.enabled`. Exposes 2 endpoints on `mgmt.listen` (address:port):

- `GET /routes` - list of all discovered routes
- `GET /metrics` - returns prometheus metrics (`http_requests_total`, `response_status` and `http_response_time_seconds`)

By default, `http_response_time_seconds` uses raw request paths as labels, which can cause high cardinality with dynamic URLs (e.g., `/api/users/123`, `/api/users/456`). Use `--mgmt.low-cardinality` to switch to route patterns (e.g., `^/api/users/(.*)`) instead, significantly reducing metrics cardinality.

_see also [examples/metrics](https://github.com/umputun/reproxy/tree/master/examples/metrics)_