feat: enhance event management functionality

[hui00]

This Pull Request introduces two significant enhancements to our event management system.

1. Add "Copy Event" button to Event Edit page with changes: We have added a new "Copy Event" (Kopieren) button on the Event Edit page. This button allows users to quickly create a duplicate of an existing event, retaining all the event details from the original, including any changes made during the edit session. This feature helps in efficient event management, especially when similar events occur frequently, by reducing the effort and time required to input the same details repeatedly.

Screenshot showing the 'Copy' button located below the 'Save' button

2. Set copied event visibility to 'false' by default: We have further enhanced the event copying function by setting the copied event's visibility to "false" (invisible) by default. This gives users more control over when a copied event becomes visible to others. A copied event now needs to be explicitly made visible, preventing any possible confusion and ensuring that only fully reviewed and ready-to-go events are visible to the public.

Screenshot showing that the visibility is set to 'false' after creating a copy

3. Display the 'Copy' button only if the event has already been created.

4. Update localization and Button Style.

5. Add improvements from the comments.

6. Add second copy button and confirmation prompt

   

7. fix spelling error
8. fix: error in changeVisibility mutation
9. refactor: simplify and js syntax
10. refactor: using jQuery to simplify code

These10 updates together aim to streamline the process of creating and managing events, leading to a more intuitive and efficient user experience.

SVA-1008