fix: read .env vars for production built

this is like a cherrypick of this pr in learning.
https://github.com/nelc/frontend-app-learning/pull/27/files
This is an error generated of the load of paragonTheme plugin.

webpack.prod.config.js

@@ -0,0 +1,18 @@
+const fs = require('fs');
+const dotenv = require('dotenv');
+const { createConfig } = require('@edx/frontend-build');
+const config = createConfig('webpack-prod');
+
+// The configuration is generated using the createConfig method from the frontend-build library,
+// this method preloads multiple files to generate the resulting configuration, including webpack.common.config.js,
+// https://github.com/nelc/frontend-build/blob/open-release/palm.nelp/config/webpack.common.config.js,
+// which includes ParagonWebpackPlugin. This plugin, in turn, retrieves its configuration from the .env.development file
+// https://github.com/nelc/frontend-build/blob/open-release/palm.nelp/lib/plugins/paragon-webpack-plugin/ParagonWebpackPlugin.js#L20-L22
+// Therefore, regardless of the configuration type, the plugin always utilizes data from .env.development.
+// The following code overrides this behavior in order to use the .env file.
+const envConfig = dotenv.parse(fs.readFileSync('.env'));
+Object.keys(envConfig).forEach(k => {
+  process.env[k] = envConfig[k];
+});
+
+module.exports = config;