Set default `cluster.routing.allocation.balance.disk_usage` (#91951)

Set the default value for `cluster.routing.allocation.balance.disk_usage`
setting to `5e-11f` that seem to have less impact on the write load
balancing results.

docs/changelog/91951.yaml

@@ -0,0 +1,5 @@
+pr: 91951
+summary: Set default `cluster.routing.allocation.balance.disk_usage`
+area: Allocation
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/cluster/routing/allocation/allocator/BalancedShardsAllocator.java

@@ -101,7 +101,7 @@ public class BalancedShardsAllocator implements ShardsAllocator {
     );
     public static final Setting<Float> DISK_USAGE_BALANCE_FACTOR_SETTING = Setting.floatSetting(
         "cluster.routing.allocation.balance.disk_usage",
-        0.0f,
+        5e-11f,
         0.0f,
         Property.Dynamic,
         Property.NodeScope