Metrics degrade cluster performance

The `/metrics` endpoint exposes Infinispan stats so that they can be periodically scraped by monitoring tools such as Prometheus. However, these stats include calls to `size` which does not perform well as the number of entries in a cache increase. Consequently, if deploying DG in a k8 environment with Prometheus monitoring the DG cluster performance rapidly declines as the number of entries in a cache increases due to time /resources spent iterating the cache container.

This problem is only exasperated when muiltiple caches exist with many entries exist.