[PUI] Plugin settings UI (#8228)

* Visual tweaks for admin pages

* Provide admin js file via API

* Backend fixes

* Tweak error detail drawer

* Refactor plugin detail panel

- Split out into separate files
- Use <Accordion />
- Display custom configuration (if available)

* Refactoring

* Add custom configuration to sample UI plugin

* Bump API version

* Add separate API endpoint for admin integration details

* Refactor plugin drawer

* Null check

* Add playwright tests for custom admin integration

* Enable plugin panels in "settings" pages

* Fix for unit test

* Hide "Plugin Settings" for plugin without "settings" mixin

* Fixes for playwright tests

* Update playwright tests

* Improved error message

src/frontend/tests/pui_settings.spec.ts

@@ -21,7 +21,7 @@ test('Admin', async ({ page }) => {
   await page.getByText('Inline report display').waitFor();
 
   // System Settings
-  await page.getByRole('link', { name: 'Switch to System Setting' }).click();
+  await page.locator('label').filter({ hasText: 'System Settings' }).click();
   await page.getByText('Base URL', { exact: true }).waitFor();
   await page.getByRole('tab', { name: 'Login' }).click();
   await page.getByRole('tab', { name: 'Barcodes' }).click();