stats: prevent disabling some stats

*Description*:
>Some stats can potentially be used for functional purposes during operation. However, the fact that they can be disabled via a stats matcher expression makes that an anti-pattern currently. We should have a mechanism to mark a stat as being immune from disabling. Since the disabling happens during stat instantiation, this would need to occur during stat construction.

*Relevant Links*:
> https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/metrics/v3/stats.proto#config-metrics-v3-statsmatcher