Added a preventDefault to the click event in GroupAvatar class

What does this MR do?

Prevents the button "choose an avatar image" from the groups form to submit it before the user can select the group avatar

Are there points in the code the reviewer needs to double check?

None at the moment

Screenshots (if relevant)

Before

After

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #26830 (closed)