Provide better performance JMX metrics for git operations

Problem Definition

The current HttpHostingStatistics and SshHostingStatistics do not provide any performance data for git clone or fetch requests.

Suggested Solution

It would be beneficial to have additional counter attributes for git clone and fetch operations that provide data on performance, like the minimum, mean and maximum request time or percentiles.

Some of this data is already available in the Bitbucket profiler log, but it would be helpful to have all this data as part of JMX monitoring.