server: enable continuous CPU profiler

This patch enables the CPU profile with a threshold of 75% and a max
frequency of 20min.

The motivation for this change is that recently, I have noticed a few
cases during investigations where CPU utilization spikes but we lack
profiles after the fact. This hinders our ability to dig deeper into the
source of high CPU usage. Having profiles can help inform us of future
AC integrations that we may need, or other performance improvements we
can do elsewhere.

Informs #97699.

Release note (ops change): CRDB will now automatically generate CPU
profiles if there is an increase in CPU utilization. This can help
investigate possible issues after the fact.

pkg/server/profiler/cpuprofiler.go

@@ -12,7 +12,6 @@ package profiler
 
 import (
 	"context"
-	"math"
 	"os"
 	"runtime/pprof"
 	"time"
@@ -41,7 +40,8 @@ var cpuUsageCombined = settings.RegisterIntSetting(
 		"the profiler will never take a profile and conversely, if a value"+
 		"of 0 is set, a profile will be taken every time the cpu profile"+
 		"interval has passed or the provided usage is increasing",
-	math.MaxInt64,
+	65,
+	settings.PositiveInt,
 )
 
 var cpuProfileInterval = settings.RegisterDurationSetting(
@@ -51,14 +51,16 @@ var cpuProfileInterval = settings.RegisterDurationSetting(
 	// account the high water mark seen. Without this, if CPU ever reaches 100%,
 	// we'll never take another profile.
 	"duration after which the high water mark resets and a new cpu profile can be taken",
-	5*time.Minute, settings.PositiveDuration,
+	20*time.Minute,
+	settings.PositiveDuration,
 )
 
 var cpuProfileDuration = settings.RegisterDurationSetting(
 	settings.ApplicationLevel,
 	"server.cpu_profile.duration",
 	"the duration for how long a cpu profile is taken",
-	10*time.Second, settings.PositiveDuration,
+	10*time.Second,
+	settings.PositiveDuration,
 )
 
 const cpuProfFileNamePrefix = "cpuprof"