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
            }
        },

[raultorrecilla]

moving this to it-106. Not critical but if we want it needs to happen in it-106

[kruskall]

the beats monitoring metric is gona and it has been migrated to an otel metric in #15094

They will still be produced to the beats monitoring registry for compatibility but since the logic for the conversation is shared this means the issue will be fixed automatically once that PR is merged.
Moved to in-review

[kruskall]

PR merged. Closing this