fix(learn): prevent indexing learn pages on search engines (#38260)

Co-authored-by: mrugesh <1884376+raisedadead@users.noreply.github.com>
Co-authored-by: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>

client/gatsby-config.js

@@ -1,4 +1,5 @@
 const path = require('path');
+const config = require('./config/env');
 
 const {
   buildChallenges,
@@ -11,7 +12,7 @@ const curriculumIntroRoot = path.resolve(__dirname, './src/pages');
 module.exports = {
   siteMetadata: {
     title: 'freeCodeCamp',
-    siteUrl: 'https://www.freecodecamp.org'
+    siteUrl: config.homeLocation
   },
   plugins: [
     'gatsby-plugin-react-helmet',

client/src/components/layouts/Learn.js

@@ -2,7 +2,7 @@ import React, { Fragment, Component } from 'react';
 import PropTypes from 'prop-types';
 import { createSelector } from 'reselect';
 import { connect } from 'react-redux';
-
+import { Helmet } from 'react-helmet';
 import { Loader } from '../../components/helpers';
 import {
   userSelector,
@@ -41,6 +41,13 @@ class LearnLayout extends Component {
     this.props.tryToShowDonationModal();
   }
 
+  componentWillUnmount() {
+    const metaTag = document.querySelector(`meta[name="robots"]`);
+    if (metaTag) {
+      metaTag.remove();
+    }
+  }
+
   render() {
     const {
       fetchState: { pending, complete },
@@ -59,6 +66,9 @@ class LearnLayout extends Component {
 
     return (
       <Fragment>
+        <Helmet>
+          <meta content='noindex' name='robots' />
+        </Helmet>
         <main id='learn-app-wrapper'>{children}</main>
         <DonateModal />
       </Fragment>