Various range load statistics such as read(write) bytes(keys) exist on
the hot ranges (v1) and range statistics api. This commit adds the
additional statistic, `CPUTimePerSecond`. This statistic is the recent
average cpu usage per second of the range in nanoseconds.

resolves: cockroachdb#95384

Release note: None

Previously, only QPS was included in the hot ranges v2 api. This commit
adds the following range statistics to the API:

```
WritesPerSecond
ReadsPerSecond
WriteBytesPerSecond
ReadBytesPerSecond
CPUTimePerSecond
```

See the associated comments in `status.proto` for a description of each
load statistic.

These may be used to determine the hottest ranges. Note however that
these are sorted by default by QPS. The ordering of ranges w.r.t the new
load statistics has no guarantees. Likewise, ranges may be omitted which
have high relative values for the new load statistics but relatively low
QPS. In practice however, there usually exists a strong correlation that
ensures that such ranges would not be omitted entirely.

resolves: cockroachdb#95383

Release note: None