changefeedccl: use numcpu >> 2 workers for event consumers

Previously, a default value of 8 was used for the kvevent parallel consumer.
The reason for this was that we observed performance improvements in a 15 node
32 VCPU cluster when we increased this parameter to 8. After 8, the
improvements were much smaller.

The issue with a default of 8 is that that on smaller machines, 8
workers can be too much overhead, especially since the work is CPU intensive.

This change updates the default to be runtime.NumCPU() >> 2 workers, which
aligns with using 8 workers on 32 VCPU machines.

Fixes cockroachdb#89589
Epic: none

Release note: None

pkg/ccl/changefeedccl/changefeedbase/settings.go

@@ -10,6 +10,7 @@ package changefeedbase
 
 import (
 	"encoding/json"
+	"runtime"
 	"time"
 
 	"github.com/cockroachdb/cockroach/pkg/settings"
@@ -239,7 +240,13 @@ var EventConsumerWorkers = settings.RegisterIntSetting(
 	settings.TenantWritable,
 	"changefeed.event_consumer_workers",
 	"the number of workers to use when processing events; 0 or 1 disables",
-	int64(util.ConstantWithMetamorphicTestRange("changefeed.consumer_max_workers", 8, 0, 32)),
+	func() int64 {
+		idealNumber := runtime.NumCPU() >> 2
+		if idealNumber < 1 {
+			return 1
+		}
+		return int64(idealNumber)
+	}(),
 	settings.NonNegativeInt,
 ).WithPublic()