feat(metrics): Add a convenience API to track metrics directly

Author: jan-auer

sentry-core/src/metrics.rs

@@ -9,6 +9,7 @@ use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
 use sentry_types::protocol::latest::{Envelope, EnvelopeItem};
 
 use crate::client::TransportArc;
+use crate::Hub;
 
 use crate::units::DurationUnit;
 pub use crate::units::MetricUnit;
@@ -344,6 +345,12 @@ impl MetricBuilder {
     pub fn finish(self) -> Metric {
         self.metric
     }
+
+    pub fn send(self) {
+        if let Some(client) = Hub::current().client() {
+            client.add_metric(self.finish());
+        }
+    }
 }
 
 pub struct MetricAggregator {