expose export offset committed avg (#221)

expose export offset committed avg for importing into internal xinfra monitor 
Signed-off-by: Andrew Choi <[email protected]>

Author: Andrew Choi

src/main/java/com/linkedin/kmf/apps/SingleClusterMonitor.java

@@ -323,6 +323,7 @@ public static void main(String[] args) throws Exception {
       "kmf.services:type=consume-service,name=*:topic-partitions-count",
       "kmf.services:type=produce-service,name=*:produce-availability-avg",
       "kmf.services:type=consume-service,name=*:consume-availability-avg",
+      "kmf.services:type=consume-service,name=*:offsets-committed-avg",
       "kmf.services:type=produce-service,name=*:records-produced-total",
       "kmf.services:type=consume-service,name=*:records-consumed-total",
       "kmf.services:type=consume-service,name=*:records-lost-total",