add redis down alert (#137)

inputs/redis/alerts.json

@@ -1,4 +1,37 @@
 [
+    {
+      "name": "Redis 节点故障",
+      "note": "",
+      "prod": "",
+      "algorithm": "",
+      "algo_params": null,
+      "delay": 0,
+      "severity": 2,
+      "disabled": 0,
+      "prom_for_duration": 30,
+      "prom_ql": "redis_up{} == 0",
+      "prom_eval_interval": 15,
+      "enable_stime": "00:00",
+      "enable_etime": "23:59",
+      "enable_days_of_week": [
+        "1",
+        "2",
+        "3",
+        "4",
+        "5",
+        "6",
+        "0"
+      ],
+      "enable_in_bg": 0,
+      "notify_recovered": 1,
+      "notify_channels": [],
+      "notify_repeat_step": 60,
+      "notify_max_number": 0,
+      "recover_duration": 0,
+      "callbacks": [],
+      "runbook_url": "",
+      "append_tags": []
+    },
     {
       "name": "Redis Ping 延迟高（大于100毫秒）",
       "note": "",
@@ -179,4 +212,4 @@
         "alertname=RedisHighKeysEvictionRatio"
       ]
     }
-  ]
+  ]