**Problem:**
- Remote reader mode only allow `project-level` Prometheus to share the
metrics from `cluster-level` Prometheus
- Remote reader mode cannot save the namespace-related metrics from
`cluster-level` Prometheus

**Solution:**
- Add `prometheus.sync.mode` to choose
- Add a "federate" scrape job when deploying federation mode

**Issue:**
https://github.com/rancher/rancher/issues/17390