Investigate replacing libbeat monitoring usage with OpenTelemetry instrumentation

[axw]

We have had issues related to libbeat monitoring plaguing us for years, notably #8383.

We should consider removing our dependency on libbeat for monitoring apm-server, and instrumenting APM Server with the OpenTelemetry API instead. We would need to arrange for the metrics to be written to the monitoring Elasticsearch cluster with the same schema as produced by libbeat; we would also need to expose these metrics via the stats API, and reported in logs.

Hat tip to @marclop for the idea.