I tried your solution but could not make it work.
I followed Adding Meta Tags section on Adding CSS & JS and Overriding the Page-Load Template and overwrote header.
Looks working now on my app on heroku.
import dash
app = dash.Dash(__name__)
app.index_string = """<!DOCTYPE html>
<html>
<head>
<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src="https://www.googletagmanager.com/gtag/js?id=UA-131327483-1"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'UA-131327483-1');
</script>
{%metas%}
<title>{%title%}</title>
{%favicon%}
{%css%}
</head>
<body>
{%app_entry%}
<footer>
{%config%}
{%scripts%}
{%renderer%}
</footer>
</body>
</html>"""