Log authenticator service call latencies

Use an express metric to log a histogram of response latency with
the intention of understanding worst case latencies and also
deliberate non-response as a keep-alive exploit.

Bug: 328990057
Test: statsd_testdrive 593
      Manually trigger AccountManager APIs by playing with apps
      containing accounts
Change-Id: I5ac07302fd382b604d3a5bf9a5f433f40a61daeb