refactor: add basic counter metrics for IMC (#5006)

crates/router_env/src/metrics.rs

@@ -120,3 +120,18 @@ macro_rules! gauge_metric {
         > = once_cell::sync::Lazy::new(|| $meter.u64_observable_gauge($description).init());
     };
 }
+
+pub use helpers::add_attributes;
+
+mod helpers {
+    pub fn add_attributes<T, U>(attributes: U) -> Vec<opentelemetry::KeyValue>
+    where
+        T: Into<opentelemetry::Value>,
+        U: IntoIterator<Item = (&'static str, T)>,
+    {
+        attributes
+            .into_iter()
+            .map(|(key, value)| opentelemetry::KeyValue::new(key, value))
+            .collect::<Vec<_>>()
+    }
+}