chore(tfstated): refactor backend code to a dedicated package

pkg/backend/healthz.go

@@ -0,0 +1,12 @@
+package backend
+
+import "net/http"
+
+func handleHealthz() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Cache-Control", "no-store, no-cache")
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte("{}"))
+	})
+}