Refactor content fetching and enhance UI mods

Refactored content fetching in the docs and blog pages to use a new 'getDocs' function to improve code reuse. Made minor adjustments to the UI in 'makerkit/page.tsx'. This involved modifying the layout and adding conditionals to tackle optional props. Also added a new textarea component reference in the UI package.

apps/web/app/(marketing)/docs/_lib/server/docs.loader.ts

@@ -0,0 +1,14 @@
+import { cache } from 'react';
+
+import { createCmsClient } from '@kit/cms';
+
+export const getDocs = cache(async (language: string | undefined) => {
+  const cms = await createCmsClient();
+
+  const { items: pages } = await cms.getContentItems({
+    collection: 'documentation',
+    language,
+  });
+
+  return pages;
+});