Provide a way to add Google Tag Manager without hacking default.html

What happened?

Minimal Mistakes version: 4.26.1
Ruby gem or remote theme version:
Jekyll version:
Git repository URL:
Hosted on GitHub Pages (if yes provide URL to site):
Operating system:

Expected behavior

Enable a way to include Google Tag Manager without having to hack default.html.

Right now you need to:

---
---

<!doctype html>
{% include copyright.html %}
<html lang="{{ site.locale | slice: 0,2 | default: "en" }}" class="no-js">
  <head>
{% if jekyll.environment == 'production' %}
{% comment %}
<script async src="https://www.googleoptimize.com/optimize.js?id=OPT-T4ZK4CX"></script>
{% endcomment %}
<!-- Google Tag Manager -->
<script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
  new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
  j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
  'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
  })(window,document,'script','dataLayer','GTM-XXX');</script>
  <!-- End Google Tag Manager -->
{% endif %}
    {% include head.html %}
    {% include head/custom.html %}
  </head>

  <body class="layout--{{ page.layout | default: layout.layout }}{% if page.classes or layout.classes %}{{ page.classes | default: layout.classes | join: ' ' | prepend: ' ' }}{% endif %}">
{% if jekyll.environment == 'production' %}
<!-- Google Tag Manager (noscript) -->
<noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-XXXX"
  height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
<!-- End Google Tag Manager (noscript) -->
{% endif %}
    {% include_cached skip-links.html %}
    {% include_cached masthead.html %}

    <div class="initial-content">
      {{ content }}
      {% include after-content.html %}
    </div>

    {% if site.search == true %}
      <div class="search-content">
        {% include_cached search/search_form.html %}
      </div>
    {% endif %}

    <div id="footer" class="page__footer">
      <footer>
        {% include footer/custom.html %}
        {% include_cached footer.html %}
      </footer>
    </div>

    {% include scripts.html %}

  </body>
</html>

Would be nice to be able to add Tag Manager without having to modify default.html, if possible.

Steps to reproduce the behavior

See above example.

Other

See above example.

mmistakes / minimal-mistakes

Provide a way to add Google Tag Manager without hacking default.html #4855

What happened?

Expected behavior

Steps to reproduce the behavior

Other