overriden: add singleton class

* Singleton class meant to manage the
  global overriden components
* closes inveniosoftware/invenio-app-rdm#2018

src/lib/index.js

@@ -1,5 +1,5 @@
 // This file is part of React-Invenio-Forms
-// Copyright (C) 2020 CERN.
+// Copyright (C) 2020, 2023 CERN.
 // Copyright (C) 2020 Northwestern University.
 //
 // React-Invenio-Forms is free software; you can redistribute it and/or modify it
@@ -8,3 +8,4 @@
 export * from "./elements";
 export * from "./forms";
 export * from "./api";
+export { overridableRegistry } from "./overridenSingleton";

src/lib/overridenSingleton.js

@@ -0,0 +1,30 @@
+// This file is part of React-Invenio-Forms
+// Copyright (C) 2023 CERN.
+//
+// React-Invenio-Forms is free software; you can redistribute it and/or modify it
+// under the terms of the MIT License; see LICENSE file for more details.
+
+let components;
+
+/**
+ * Singleton class to provide a global access point to the overriden components
+ */
+class OverridenSingleton {
+  constructor() {
+    if (!OverridenSingleton.instance) {
+      OverridenSingleton.instance = this;
+    }
+
+    return OverridenSingleton.instance;
+  }
+
+  getComponents() {
+    return components;
+  }
+
+  addComponents(newComponents) {
+    components = { ...components, ...newComponents };
+  }
+}
+
+export const overridableRegistry = new OverridenSingleton();