stats: add a config options that allow to disable all counters, gauges, histograms

*Title*: *Add a config options that allow to disable all counters, gauges, histograms*

*Description*:
The feature could be useful in general but it's especially interesting from the perspective of mobile clients. Since the aggregation of gauges and histogram data across millions of mobile clients is a non trivial thing to do it may be pretty common for the users of Envoy Mobile to want to disable all gauges and/or histograms to save on CPU/mem/data bandwidth usage.