Test plugins: Add datasource test plugin with field tests (#95472)

* add new test plugin

* add some field validation tests

* update lockfile

* fix bad test file name

e2e/plugin-e2e/plugin-e2e-api-tests/as-admin-user/dashboard.spec.ts

@@ -0,0 +1,15 @@
+import { expect, test } from '@grafana/plugin-e2e';
+
+const REACT_TABLE_DASHBOARD = { uid: 'U_bZIMRMk' };
+
+test('add panel in already existing dashboard', async ({ gotoDashboardPage, page }) => {
+  const dashboardPage = await gotoDashboardPage(REACT_TABLE_DASHBOARD);
+  await dashboardPage.addPanel();
+  await expect(page.url()).toContain('editPanel');
+});
+
+test('add panel in new dashboard', async ({ dashboardPage, page }) => {
+  const panelEditPage = await dashboardPage.addPanel();
+  await expect(panelEditPage.panel.locator).toBeVisible();
+  await expect(page.url()).toContain('editPanel');
+});