Increase replica_unassigned_buffer_time default from 3s to 5s (#112834)

Increase the default value of health.shards_availability.replica_unassigned_buffer_time to 5 seconds. This values in the identification of unavailable shards on serverless. Increasing the value to 5s keep more shards from going red transiently, while still being low enough to go red quickly if there is an actual availability issue.

Related to #112066

Author: parkertimmins

docs/changelog/112834.yaml

@@ -0,0 +1,5 @@
+pr: 112834
+summary: Increase `replica_unassigned_buffer_time` default from 3s to 5s
+area: Health
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/cluster/routing/allocation/shards/ShardsAvailabilityHealthIndicatorService.java

@@ -120,7 +120,7 @@ public class ShardsAvailabilityHealthIndicatorService implements HealthIndicator
      */
     public static final Setting<TimeValue> REPLICA_UNASSIGNED_BUFFER_TIME = Setting.timeSetting(
         "health.shards_availability.replica_unassigned_buffer_time",
-        TimeValue.timeValueSeconds(3),
+        TimeValue.timeValueSeconds(5),
         TimeValue.timeValueSeconds(0),
         TimeValue.timeValueSeconds(20),
         Setting.Property.NodeScope,