feat(timer): 新增配置同步到数据库及主节点选举

T5: TimerServiceBase.syncConfigToDatabase() - syncs task config to DB
T6: HostServiceBase - auto master election, stale node detection,
    getMasterNode/setMasterNode methods

app/admin/model/SystemTimerConfig.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace app\admin\model;
+
+use think\Model;
+
+class SystemTimerConfig extends Model
+{
+    protected $name = 'system_timer_config';
+
+    protected $autoWriteTimestamp = true;
+}