Minor correction needed to details on the automatic CPU profiler

Affected page: https://www.cockroachlabs.com/docs/stable/automatic-cpu-profiler#high-water-mark-threshold

What needs changed:

At `time2`, the `20m0s` interval after `time0`, the high-water mark threshold is reset to the baseline threshold of `65`.

Needs to be changed to this line:

At `time2`, the `20m0s` interval after `time1`, the high-water mark threshold is reset to the baseline threshold of `65`.

Reasoning:

The interval period always resets after each new CPU profile, so we count the 20 minutes from `time1` in this example - we do NOT count from when the first CPU profile was taken.

Confirmation:

Confirmed by the Observability team and by the code in https://github.com/cockroachdb/cockroach/blob/74a9fdc34d97afc902379f73f017e028531ae841/pkg/server/profiler/profiler_common.go#L113

Jira issue: DOC-16188