monitoring: Agentcfg monitoring metric names contain dot

[carsonip]

Looking at apm-server:5066/stats, agentcfg is an outlier that it contains metrics that have dots in the name, unlike other metrics that are all nested.

        "agentcfg": {
            "elasticsearch": {
                "cache.entries.count": 0,
                "cache.refresh.failures": 0,
                "cache.refresh.successes": 220,
                "fetch.es": 0,
                "fetch.fallback": 0,
                "fetch.invalid": 0,
                "fetch.unavailable": 0
            }
        },