Record the clock frequency in the optrack log file, so we can convert CPU cycles to nanoseconds when decoding the files.

Currently the operation tracking code records the timestamps in units of CPU cycles, because that's the most efficient way to do things. However, showing the timeline to the user in units of CPU cycles is not the most convenient. We should take advantage of the nanoseconds-to-cycles conversion ratio computed within the WT library and record this ratio in the log file. This way, we can convert cycles to nanoseconds upon conversion and display the trace to the user using a more standard time metric.