Function initialize_metrics 

pub async fn initialize_metrics(
    metrics_prefix: String,
    default_level: Level,
) -> Result<(FilterHandle, MetricsFlusherWorker), GenericError>

Initializes the metrics subsystem with the given metrics prefix and default filter level.

default_level sets the initial filter level for emitted metrics, and is also what the filter is restored to when FilterHandle::reset_filter is invoked. Metrics whose level is more verbose than this default are filtered out until a runtime override is applied via FilterHandle::override_filter.

Returns a FilterHandle for adjusting the runtime metrics filter, plus a MetricsFlusherWorker that must be added to a Supervisor in order to drive the periodic flush loop. Internal metrics aren’t propagated to subscribers until the worker is running.

Errors

If a global recorder was already installed, an error will be returned.