feat: add metrics support

internal/metrics/server.go

@@ -0,0 +1,14 @@
+package metrics
+
+import (
+	"net/http"
+)
+
+func Handler() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/plain")
+		for k, v := range metrics {
+			w.Write([]byte(k + " " + string(v) + "\n"))
+		}
+	})
+}