sql: track CPU time on gateway node

[jordanlewis]

Updates #87213

This commit adds a new field to the statement_statistics, which is the number of CPU seconds spent (on the gateway node only) processing a particular SQL query.

It uses the new "grunning" CPU seconds tracker to calculate this quantity.

Release note (sql change): add the cpu_time_avg and cpu_time_var fields to crdb_internal.node_statement_statistics, and the cpu_time field to the statistics JSON in system.statement_statistics.

[cockroach-teamcity]

This change is 

[maryliag]

If this is just playing around, ignore my comments, otherwise I added a few nits and this would also need tests added.

Reviewed 12 of 12 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @jordanlewis)

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pkg/roachpb/app_stats.proto line 117 at r1 (raw file):

  // cpu_time is the amount of CPU time spent (in seconds) by this query.
  optional NumericStat cpu_time = 28 [(gogoproto.nullable) = false];

nit: you're calling this CPU time in a few places and service CPU time in others, make sure is consistent

add (gogoproto.customname) = "CPUTime"

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pkg/sql/sessionphase/session_phase.go line 59 at r1 (raw file):

	PlannerEndExecStmt

	PlannerEndExecStmtCpuTime

nit: PlannerEndExecStmtCPUTime

[jordanlewis]

Thanks to @DrewKimball, this is obviated by #93952!

[DrewKimball]

I used this as my starting point BTW