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

playwright.config.ts

@@ -97,6 +97,15 @@ export default defineConfig<PluginOptions>({
       },
       dependencies: ['authenticate'],
     },
+    {
+      name: 'grafana-e2etest-datasource',
+      testDir: 'e2e/test-plugins/grafana-test-datasource',
+      use: {
+        ...devices['Desktop Chrome'],
+        storageState: 'playwright/.auth/admin.json',
+      },
+      dependencies: ['authenticate'],
+    },
     {
       name: 'cloudwatch',
       testDir: path.join(testDirRoot, '/cloudwatch'),