subsystem-benchmarks: estimate reference hardware CPU usage

[sandreim]

In CI we need to run the benchmarks on ref hardware machines, but development is usually done on faster machines. I think it would be both interesting and useful to consider reporting some estimations for reference hardware.

One idea is to bundle the polkadot node benchmark in the CLI tool and run it once to get the following metrics:Blake2256, Sr25519Verify, MemCopy. We then use these metrics to compute a perf_index coefficient . Assuming we have determined a similar value for the reference hardware we can the estimate CPU usage from the results of the local development machine:
estimated_ref_hw_cpu = local_perf_index / ref_perf_index * local_cpu_usage