Add dropdown to navigation links

- add download page
- move main pages tests to their own folder
- add download and public eng snapshot test
- remove public engagement button on each page
- swap index with cejst
- update cypress ENDPOINTS
- upate gatsby-config sitemap
- update snapshots
- cypress tests are failing

client/src/pages/tests/downloads.test.tsx

@@ -0,0 +1,16 @@
+import * as React from 'react';
+import {render} from '@testing-library/react';
+import {LocalizedComponent} from '../../test/testHelpers';
+import DownloadsPage from '../downloads';
+
+describe('rendering of the DatasetContainer', () => {
+  const {asFragment} = render(
+      <LocalizedComponent>
+        <DownloadsPage location={window.location}/>
+      </LocalizedComponent>,
+  );
+
+  it('checks if various text fields are visible', () => {
+    expect(asFragment()).toMatchSnapshot();
+  });
+});