✨(frontend) added subpage management and document tree features

New components were created to manage subpages in the document tree,
including the ability to add, reorder, and view subpages. Tests were
added to verify the functionality of these features. Additionally, API
changes were made to manage the creation and retrieval of document
children.

src/frontend/apps/e2e/__tests__/app-impress/doc-create.spec.ts

@@ -14,10 +14,10 @@ test.beforeEach(async ({ page }) => {
 
 test.describe('Doc Create', () => {
   test('it creates a doc', async ({ page, browserName }) => {
-    const [docTitle] = await createDoc(page, 'My new doc', browserName, 1);
+    const [docTitle] = await createDoc(page, 'my-new-doc', browserName, 1);
 
     await page.waitForFunction(
-      () => document.title.match(/My new doc - Docs/),
+      () => document.title.match(/my-new-doc - Docs/),
       { timeout: 5000 },
     );