Add Plausible for docs metrics

[hugovk]

We're going to continue using Plausible for stats. The account is ready, let's merge this so we can begin collecting stats, and then look into one of the options suggested at #107136.

---

📚 Documentation preview 📚: https://cpython-previews--119977.org.readthedocs.build/

[JulienPalard]

Something like this could prevent plausible to land on HTML builds distributed out of docs.python.org (like linux distribs):

--- a/Doc/conf.py
+++ b/Doc/conf.py
@@ -339,7 +339,8 @@
 html_context = {
     "is_deployment_preview": os.getenv("READTHEDOCS_VERSION_TYPE") == "external",
     "repository_url": repository_url.removesuffix(".git") if repository_url else None,
-    "pr_id": os.getenv("READTHEDOCS_VERSION")
+    "pr_id": os.getenv("READTHEDOCS_VERSION"),
+    "enable_analytics": os.getenv("PYTHON_DOCS_ENABLE_ANALYTICS"),
 }
 
 # This 'Last updated on:' timestamp is inserted at the bottom of every page.

--- a/Doc/tools/templates/layout.html
+++ b/Doc/tools/templates/layout.html
@@ -26,7 +26,7 @@
 {% endblock %}
 
 {% block extrahead %}
-    {% if builder == "html" %}
+    {% if builder == "html" and enable_analytics %}
       <script defer data-domain="docs.python.org" src="https://plausible.io/js/script.js"></script>
     {% endif %}
     <link rel="canonical" href="https://docs.python.org/3/{{pagename}}.html" />

[hugovk]

Thanks for the diff! I've added that to the PR, and verified locally the snippet only shows in the HTML when building with the env var set.

[hugovk]

Merging to give a chance to be deployed. It won't be active until the env var is set by python/psf-salt#357.

[miss-islington-app]

Thanks @hugovk for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

[bedevere-app]

GH-120193 is a backport of this pull request to the 3.13 branch.

[bedevere-app]

GH-120194 is a backport of this pull request to the 3.12 branch.