chore: import upstream snapshot with attribution

docs/source/_templates/versioning.html

@@ -0,0 +1,65 @@
+{% if versions %}
+
+<!-- Start of versioning -->
+
+<div class="sidebar-tree">
+    <p class="caption" role="heading">
+        <span class="caption-text">{{ _('Versions') }}</span>
+    </p>
+    <ul>
+        <li class="toctree-l1">
+            <a
+                id="version_number"
+                class="reference internal"
+                href="{{ DOCS_SITE_URL }}"
+                >stable</a
+            >
+        </li>
+        <li class="toctree-l1">
+            <a
+                id="commit_hash"
+                class="reference internal"
+                href="{{DOCS_SITE_URL}}master/"
+                >developer</a
+            >
+        </li>
+        {% for version in RELEASE_VERSIONS %}
+        <li class="toctree-l1">
+            <a
+                id="{{ version }}"
+                class="reference internal"
+                href="{{DOCS_SITE_URL}}{{version}}/"
+                >{{version}}</a
+            >
+        </li>
+        {% endfor %}
+    </ul>
+</div>
+
+<br>
+<br>
+
+<script
+    type="text/javascript"
+    src="{{ DOCS_SITE_URL }}versioning.js"
+></script>
+
+<script type="text/javascript">
+    window.addEventListener("load", () => {
+        const version_number = Version.version_number;
+        const commit_hash = Version.commit_hash;
+
+        document.getElementById("version_number").innerHTML =
+            "stable <code class='docutils literal notranslate'><span class='pre'> (" +
+            version_number +
+            ")</span></code>";
+        document.getElementById("commit_hash").innerHTML =
+            "master <code class='docutils literal notranslate'><span class='pre'> (" +
+            commit_hash.slice(0, 7) +
+            "&hellip;)</span></code>";
+    });
+</script>
+
+<!-- End of versioning -->
+
+{% endif %}