feat: add byo react package netlify-cms-app (#2252)

packages/netlify-cms-app/webpack.config.js

@@ -0,0 +1,25 @@
+const path = require('path');
+const webpack = require('webpack');
+const pkg = require('./package.json');
+const { getConfig, plugins } = require('../../scripts/webpack');
+const baseWebpackConfig = getConfig({ baseOnly: true });
+
+const isProduction = process.env.NODE_ENV === 'production';
+console.log(`${pkg.version}${isProduction ? '' : '-dev'}`);
+
+const baseConfig = {
+  ...baseWebpackConfig,
+  context: path.join(__dirname, 'src'),
+  entry: './index.js',
+  plugins: [
+    ...Object.entries(plugins)
+      .filter(([key]) => key !== 'friendlyErrors')
+      .map(([, plugin]) => plugin()),
+    new webpack.DefinePlugin({
+      NETLIFY_CMS_VERSION: JSON.stringify(`- app - ${pkg.version}${isProduction ? '' : '-dev'}`),
+      NETLIFY_CMS_CORE_VERSION: null,
+    }),
+  ],
+};
+
+module.exports = baseConfig;