Improve Metric Name Generation to Include Parent Metric Name in Nested Scenarios

[tpeczek]

In scenario like the one below, the library could autmatically generate metric names which reflect the nesting (e.g. OuterCallName.InnerCallName).

using (_serverTiming.TimeAction("OuterCallName"))
{
  setup();
  using (_serverTiming.TimeAction("InnerCallName "))
  {
    doSomeWork();
  }
  otherstuff();
}

This behaviour should be optional to maintaine backward compatibility.