Collect multiple trace samples from a single benchmark run

**Add a pointer to any prior users list discussion.**
Currently we can collect one trace sample during a benchmark run. We use '-trace_after_instrs' and '-exit_after_tracing' to select a trace point.

**Is your feature request related to a problem? Please describe.**
We need to run the benchmark multiple times to collect traces throughout the benchmark execution. For long running benchmark, this may take a very long time.

**Describe the solution you'd like**
Have a way to ‘trace x million insts every y million insts’. A more advanced method would be to have a config file listing the sampling windows.

Do you have any implementation in mind for this feature?
No

**Describe alternatives you've considered**
Currently we plan to run the benchmark with a diff sampling point.

**Additional context**
None.