add 100th percentile for session_idle_time

Summary: Adding 100th percentile for session_idle_time -- the idle time between two consecutive transactions, so that we can have better idea on how conn_idle_timeout will be hit or not

Reviewed By: kwaugh

Differential Revision: D78777892

fbshipit-source-id: 57825c1816def1c0b0b274b69292cbef3c38eec9

Author: Rongxin Xia

proxygen/lib/http/stats/ThreadLocalHTTPSessionStats.cpp

@@ -58,7 +58,8 @@ TLHTTPSessionStats::TLHTTPSessionStats(const std::string& prefix)
                       50,
                       75,
                       95,
-                      99),
+                      99,
+                      100),
       ctrlMsgsInInterval(
           prefix + "_ctrl_msgs_in_interval",
           1 /* bucketWidth */,