Upgrade react-admin to version 5 (#40)

* wip on ra upgrade

* Finish upgrade

* fix package.json

* pr fixes

* more pr fixes

* update readme

src/App.test.tsx

@@ -1,4 +1,6 @@
-import { render, screen } from "@testing-library/react";
+import { render, screen, waitFor } from "@testing-library/react";
+import fetchMock from "jest-fetch-mock";
+fetchMock.enableMocks();
 
 import App from "./App";
 
@@ -7,4 +9,4 @@ describe("App", () => {
     render(<App />);
     await screen.findAllByText("Welcome to Synapse-admin");
   });
-});
+});