Benchmark monitoring dashboards using Datadog

Context

On master, thanks to NXP-28695, the DataDog reporter is now built-in and exposes much more relevant metrics.
Let's use this in the context of the benchmark.

Goals

So far, for most benchmarks, we did we used other tools than DataDog to handle the monitoring.
This time, since we are benchmarking an NCO based infrastructure, I think this is critical that we use only DataDog as a way to monitor the benchmark.

This approach should maximize our investment in DD:

• consistency: we all use the same tools
• create valuable dashboards that can be reused by the NCO team