[TracesHostInfo] Only produce metric for instances generating application metrics

[jcreixell]

The traces_host_info metric should only be produced for hosts generating application telemetry (specifically, spanmetrics and servicegraph), and stop being produced when the host no longer produces such metrics.

At the moment, the prometheus implementation behaves correctly in the sense that is wrapped in an expirer and only updated when consuming a span.

The OTEL implementation does not follow this pattern and always exposes the metric, regardless on whether spans have been consumed or not.