Fix the following issue:
proposal: profiler: add CPUProfileRate option
Calling runtime.SetCPUProfileRate with a non-zero value starts profiling at the given rate, if it hasn't already been called. This rate is effective until profiling is stopped (by setting the rate to 0). Because the profiler continually starts and stops CPU profiling, every round of CPU profiling after the first one will instead run with the default rate of 100 Hz. The user has no way to change this other than completely stopping our profiling. We should have a profiler option to give a rate that will be set each time before CPU profiling is started.