Move "Time Spent in IMAP-*" Log Entry from INFO to DEBUG

At logging INFO level the logs have a tremendous number of imap metrics lines:

org.apache.james.metrics.logger.DefaultMetricFactory | Time spent in IMAP-FETCH: 53 ms.

To me this seems more like a DEBUG level log entry.  Obviously a matter of opinion.  But I like to think of INFO level as more 'one-time' entries rather than multiple repetitive heartbeat-type log entries.

Simply recommending changing the log level on that entry from INFO to DEBUG. 

I can make the change and submit a pull request if no objections.