[enhancement](fe-memory) support label num threshold to reduce fe memory consumption (#22889)

Co-authored-by: Yongqiang YANG <98214048+dataroaring@users.noreply.github.com>

fe/fe-common/src/main/java/org/apache/doris/common/Config.java

@@ -2414,4 +2414,13 @@ public class Config extends ConfigBase {
         "The max number work threads of http upload submitter."
     })
     public static int http_load_submitter_max_worker_threads = 2;
+
+    @ConfField(mutable = true, masterOnly = true, description = {
+            "load label个数阈值，超过该个数后，对于已经完成导入作业或者任务，其label会被删除，被删除的 label 可以被重用。",
+            "The threshold of load labels' number. After this number is exceeded, "
+                    + "the labels of the completed import jobs or tasks will be deleted, "
+                    + "and the deleted labels can be reused."
+    })
+    public static int label_num_threshold = 2000;
+
 }