website/docs: Improved Version Picker. (#14404)

* website: Flesh out version picker. Port 3.8 theme.

* website: Update Dockerfile to include compose.

* website: Flesh out branch override. Tidy list items.

website/docusaurus-theme/theme/DocSidebarItems/index.tsx

@@ -0,0 +1,26 @@
+/// <reference types="@docusaurus/plugin-content-docs" />
+import { VersionPicker } from "#components/VersionPicker/index.tsx";
+
+import {
+    DocSidebarItemsExpandedStateProvider,
+    useVisibleSidebarItems,
+} from "@docusaurus/plugin-content-docs/client";
+import DocSidebarItem from "@theme/DocSidebarItem";
+import type { Props as DocSidebarItemsProps } from "@theme/DocSidebarItems";
+import { memo } from "react";
+
+const DocSidebarItems = ({ items, ...props }: DocSidebarItemsProps): JSX.Element => {
+    const visibleItems = useVisibleSidebarItems(items, props.activePath);
+    const includeVersionPicker = props.level === 1 && !props.activePath.startsWith("/integrations");
+
+    return (
+        <DocSidebarItemsExpandedStateProvider>
+            {includeVersionPicker ? <VersionPicker /> : null}
+            {visibleItems.map((item, index) => (
+                <DocSidebarItem key={index} item={item} index={index} {...props} />
+            ))}
+        </DocSidebarItemsExpandedStateProvider>
+    );
+};
+
+export default memo(DocSidebarItems);