Add Hubspot tracking code to other domains

[zachaysan]

Based on an investigation into Hubspot not properly tracking usage I believe we need to add the below to our primary domains (definitely app.flagsmith.com and docs.flagsmith.com, but check if we have other subdomains.) The script should be running on every page for flagsmith.com

<!-- Start of HubSpot Embed Code -->
<script type="text/javascript" id="hs-script-loader" async defer src="//js-eu1.hs-scripts.com/143451822.js"></script>
<!-- End of HubSpot Embed Code -->