Publish EL Info in Metrics (#7052)

Since we now know the EL version, we should publish this to our metrics periodically.

beacon_node/execution_layer/src/engine_api/http.rs

@@ -1242,6 +1242,10 @@ impl HttpJsonRpc {
         } else {
             let engine_version = self.get_client_version_v1().await?;
             *lock = Some(CachedResponse::new(engine_version.clone()));
+            if !engine_version.is_empty() {
+                // reset metric gauge when there's a fresh fetch
+                crate::metrics::reset_execution_layer_info_gauge();
+            }
             Ok(engine_version)
         }
     }