[Opt](heartbeat) improve the tolerance of the cluster to occasional h…

…eartbeat failures (apache#38896)

To improve the tolerance of the cluster to occasional heartbeat
failures，change max_backend_heartbeat_failure_tolerance_count from 1 to
3.

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

@@ -1923,12 +1923,12 @@ public class Config extends ConfigBase {
 
     /**
      * Maximum backend heartbeat failure tolerance count.
-     * Default is 1, which means if 1 heart failed, the backend will be marked as dead.
+     * Default is 3, which means if 3 heart failed, the backend will be marked as dead.
      * A larger value can improve the tolerance of the cluster to occasional heartbeat failures.
      * For example, when running regression tests, this value can be increased.
      */
     @ConfField(mutable = true, masterOnly = true)
-    public static long max_backend_heartbeat_failure_tolerance_count = 1;
+    public static long max_backend_heartbeat_failure_tolerance_count = 3;
 
     /**
      * Abort transaction time after lost heartbeat.

fe/fe-core/src/test/java/org/apache/doris/clone/TabletHealthTest.java

@@ -61,6 +61,7 @@ protected void beforeCreatingConnectContext() throws Exception {
         Config.colocate_group_relocate_delay_second = -1000; // be dead will imm relocate
         Config.tablet_schedule_interval_ms = 7200_000L;  //disable schedule
         Config.tablet_checker_interval_ms = 7200_000L;  //disable checker
+        Config.max_backend_heartbeat_failure_tolerance_count = 1;
     }
 
     @Override