add document for persistentProbeResult in backgroundObservatory

Author: xiaokangwang

docs/en_US/config/service/backgroundObservatory.md

@@ -14,3 +14,8 @@ The URL to send probe request to.
 > `probeInterval`: number
 
 The time between each probe in second.
+
+> `persistentProbeResult`: bool
+
+Whether to store probe result in persistent storage. (v5.27.0+)
+This requires persistent storage support.

docs/v5/config/service/backgroundObservatory.md

@@ -19,3 +19,8 @@
 > `probeInterval`: number
 
 发起探测的间隔。每经过这个时间，就会对一个服务器进行服务器状态检测。时间格式为数字+单位，比如`"10s"`, `"2h45m"`，支持的时间单位有 `ns`, `us`, `ms`, `s`, `m`, `h`， 分别对应纳秒、微秒、毫秒、秒、分、时。
+
+> `persistentProbeResult`: bool
+
+是否将探测结果存储在持久存储中。(v5.27.0+)
+依赖于持久存储模块。