Made perf counter changes

It feels like this is a lot of work to do on each iteration, especially knowing that the list of counters to be sampled isn't going to change. I thought the intent of the Json blob was to allow us to add counters without having to change the schema, not to replicate the metadata for each counter in each sample.

If we stored the metadata separately, we should be able to define the mappings once instead of each time we sample.