[enhance](blacklist) seperate blacklist conf from heartbeat (#28638)

There is a circuit breaker lasting for 2 minutes in grpc, then if a be is down and up again, send fragments to the be fails lasting for 2 minutes.

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

@@ -1782,6 +1782,20 @@ public class Config extends ConfigBase {
     @ConfField(mutable = true, masterOnly = true)
     public static long max_backend_heartbeat_failure_tolerance_count = 1;
 
+    /**
+     * Heartbeat interval in seconds.
+     * Default is 10, which means every 10 seconds, the master will send a heartbeat to all backends.
+     */
+    @ConfField(mutable = false, masterOnly = false)
+    public static int heartbeat_interval_second = 10;
+
+    /**
+     * After a backend is marked as unavailable, it will be added to blacklist.
+     * Default is 120.
+     */
+    @ConfField(mutable = true, masterOnly = false)
+    public static int blacklist_duration_second = 120;
+
     @ConfField(mutable = true, masterOnly = false, description = {
             "禁止创建odbc, mysql, broker类型的外表", "Disallow the creation of odbc, mysql, broker type external tables"})
     public static boolean enable_odbc_mysql_broker_table = false;