🥅(frontend) improve add member form error handling

- translate known errors, including already existing
group error, and directly display the other ones
- add component tests
- update translations
- add parseAPIError, a reusable function to
catch errors on the whole frontend app

Closes issue #293

♻️(frontend) improve general error catching

- change parseAPIError to make it reusable on all
requests
- update components depending on it

src/frontend/apps/e2e/__tests__/app-desk/teams-create.spec.ts

@@ -108,7 +108,9 @@ test.describe('Teams Create', () => {
     await page.getByRole('button', { name: 'Create the team' }).click();
 
     await expect(
-      page.getByText('Team with this Slug already exists.'),
+      page.getByText(
+        'This name is already used for another group. Please enter another one.',
+      ),
     ).toBeVisible();
   });