AiO: Add E2E test for user notification on fatal template validation errors

[bfrgottscma]

Add E2E test for: As a user I would like to be notified if my uploaded AiO template is not correct. Currently, a toaster is triggered upon loading an incorrect file Error message begins with: Invalid data format. Please select an .xlsx file with the correct format (FCL All-in-one template)!

Data upload is cancelled as those errors are fatal.

• Test for success, message does not appear
• Test for one fatal case, message appears

Think of Tests

• Excel testsheet: AiO-Template_Minimalbeispiel_20240517.xlsx
• [x] E2e test needed
• [ ] Integration test needed
• [ ] Unit test needed

Additional context

• [ ] Mockup needed