core: Add a periodic donation request (#8981)

Will fire once in december and july. Disableable with `ecosystem:no_donation:nag`

src/managers/DonationNagManager.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <memory>
+
+class CDonationNagManager {
+  public:
+    CDonationNagManager();
+
+    // whether the donation nag was shown this boot.
+    bool fired();
+
+  private:
+    bool m_bFired = false;
+};
+
+inline std::unique_ptr<CDonationNagManager> g_pDonationNagManager;