branch-4.0: [fix](fe) cloud replica use one Random object to reduce memory #59320 (#59373)

Cherry-picked from #59320

Co-authored-by: meiyi <[email protected]>

Author: github-actions[bot]

fe/fe-core/src/main/java/org/apache/doris/cloud/catalog/CloudReplica.java

@@ -67,7 +67,7 @@ public class CloudReplica extends Replica {
     @SerializedName(value = "idx")
     private long idx = -1;
 
-    private Random rand = new Random();
+    private static final Random rand = new Random();
 
     private Map<String, List<Long>> memClusterToBackends = new ConcurrentHashMap<String, List<Long>>();