net: record TCP BBR congestion algorithm stats

If we enable the BBR congestion control algorithm in Cloud and/or recommend self-hosted clusters use BBR, then we should collect BBR-specific metrics. See [this internal doc](https://docs.google.com/document/d/1QiHVXJCWShzieVY2Fe3tE9VndbVlI3ETgU4s7NPXuJw/edit?tab=t.0) for more details.

These metrics should be relatively easy to access once #149959 is completed:

https://github.com/mikioh/tcpinfo/blob/30a79bb1804bc47fa7fe29928c9109f368792a9e/zsys_linux.go#L97-L103

```
type tcpBBRInfo struct {
Bw_lo uint32
Bw_hi uint32
Min_rtt uint32
Pacing_gain uint32
Cwnd_gain uint32
}
```

We might not need all of these. We should figure out which metrics are best to capture to understand the behavior of BBR in a production cluster.

Jira issue: CRDB-53120