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/test-plugins/grafana-test-datasource/webpack.config.ts

@@ -0,0 +1,44 @@
+import CopyWebpackPlugin from 'copy-webpack-plugin';
+import grafanaConfig from '@grafana/plugin-configs/webpack.config';
+import { mergeWithCustomize, unique } from 'webpack-merge';
+import { Configuration } from 'webpack';
+
+function skipFiles(f: string): boolean {
+  if (f.includes('/dist/')) {
+    // avoid copying files already in dist
+    return false;
+  }
+  if (f.includes('/node_modules/')) {
+    // avoid copying tsconfig.json
+    return false;
+  }
+  if (f.includes('/package.json')) {
+    // avoid copying package.json
+    return false;
+  }
+  return true;
+}
+
+const config = async (env: Record<string, unknown>): Promise<Configuration> => {
+  const baseConfig = await grafanaConfig(env);
+  const customConfig = {
+    plugins: [
+      new CopyWebpackPlugin({
+        patterns: [
+          // To `compiler.options.output`
+          { from: 'README.md', to: '.', force: true },
+          { from: 'plugin.json', to: '.' },
+          { from: 'CHANGELOG.md', to: '.', force: true },
+          { from: '**/*.json', to: '.', filter: skipFiles },
+          { from: '**/*.svg', to: '.', noErrorOnMissing: true, filter: skipFiles }, // Optional
+        ],
+      }),
+    ],
+  };
+
+  return mergeWithCustomize({
+    customizeArray: unique('plugins', ['CopyPlugin'], (plugin) => plugin.constructor && plugin.constructor.name),
+  })(baseConfig, customConfig);
+};
+
+export default config;