website/docs: Update Docusaurus config. Prep for version picker. (#14401)

* website/docs: Clean up config. Add types.

* website/docs: Format MDX.

* website: Fix build warnings. Lint badges frontmatter.

website/remark/preview-directive.mjs

@@ -0,0 +1,47 @@
+/**
+ * @file Remark plugin to transform `ak-preview` directives into preview badges.
+ *
+ * @import { Root } from "mdast";
+ */
+import { h } from "hastscript";
+import { SKIP, visit } from "unist-util-visit";
+
+/**
+ * MDAST plugin to transform `ak-preview` directives into preview badges.
+ */
+function remarkPreviewDirective() {
+    /**
+     * @param {Root} tree The MDAST tree to transform.
+     */
+    return function (tree) {
+        visit(tree, "textDirective", function (node) {
+            if (node.name !== "ak-preview") return SKIP;
+
+            const data = node.data || (node.data = {});
+
+            const hast = h("span", {
+                ...node.attributes,
+                "className": "badge badge--preview",
+                "title": `This feature is in preview and may change in the future.`,
+                "aria-description": "Preview badge",
+                "role": "img",
+            });
+
+            data.hName = hast.tagName;
+            data.hProperties = hast.properties;
+
+            data.hChildren = [
+                {
+                    type: "text",
+                    value: "Preview",
+                },
+            ];
+
+            node.children = [];
+
+            return SKIP;
+        });
+    };
+}
+
+export default remarkPreviewDirective;