Add uniqueness check to "Create project" command (#5100)

* Add failing playwright test

* Make create generate a unique name if the given one collides

* Add a new consolidated getUniqueProjectName function with tests

* Use getUniqueProjectName

* Replace "New project" button text with "Create project"
cc @pierremtb

* Extend the e2e test to show the incrementing behavior
cc @lf94

e2e/playwright/code-pane-and-errors.spec.ts

@@ -280,7 +280,7 @@ test(
 
       await expect(page.getByRole('link', { name: 'bracket' })).toBeVisible()
       await expect(page.getByText('router-template-slate')).toBeVisible()
-      await expect(page.getByText('New Project')).toBeVisible()
+      await expect(page.getByText('Create project')).toBeVisible()
     })
 
     await test.step('Opening the router-template project should load', async () => {