MINOR: sample: add cpu_calls, cpu_ns_avg, cpu_ns_tot, lat_ns_avg, lat_ns_tot

MINOR: sample: add cpu_calls, cpu_ns_avg, cpu_ns_tot, lat_ns_avg, lat_ns_tot

These sample fetch keywords report performance metrics about the task calling
them. They are useful to report in logs which requests consume too much CPU
time and what negative performane impact it has on other requests. Typically
logging cpu_ns_avg and lat_ns_avg will show culprits and victims.