UI: Add update checks (#715)

src/dusk/http/no_backend.cpp

@@ -0,0 +1,24 @@
+#include "http.hpp"
+
+namespace dusk::http {
+
+bool available() noexcept {
+    return false;
+}
+
+Backend backend() noexcept {
+    return Backend::None;
+}
+
+const char* backend_name() noexcept {
+    return "none";
+}
+
+Result get(const Request&) {
+    return {
+        .error = Error::NoBackend,
+        .message = "No HTTP backend is available",
+    };
+}
+
+}  // namespace dusk::http