fix: hardcode the newrelic agent, to load it earlier (#652)

This is a test, before making a more proper fix in frontend-build.
But I'd like to confirm this fixes some issues we've seen with
newrelic metrics.

AA-1015

webpack.prod.config.js

@@ -0,0 +1,18 @@
+const { getBaseConfig } = require('@edx/frontend-build');
+
+const config = getBaseConfig('webpack-prod');
+
+// Filter plugins in the preset config that we don't want
+function filterPlugins(plugins) {
+  const pluginsToRemove = [
+    'a', // "a" is the constructor name of HtmlWebpackNewRelicPlugin
+  ];
+  return plugins.filter(plugin => {
+    const pluginName = plugin.constructor && plugin.constructor.name;
+    return !pluginsToRemove.includes(pluginName);
+  });
+}
+
+config.plugins = filterPlugins(config.plugins);
+
+module.exports = config;