06 Let save character as favorite

[github-actions]

Description

On the detailed characters page, a button indicates, that you can save the rendered character as a favorite. When the button is clicked, the character is saved as a favorite and the button indicates that. When clicked again, the character is removed as a favorite.

ToDos

• move this issue in the board from ToDo tab into In Progress tab
• create a new branch locally
• add a favorite button
• when the character is not saved as a favorite yet, the button indicates that with a neutral color
• when clicking the button, the character is saved as a favorite and the button indicates that with a signal (maybe green color)
• when clicked again, the character is removed as a favorite, the color of the button changes again
• the favorite state should persist, when the app is reloaded. (localStorage)
• commit everything
• push everything to the remote repo on GitHub
• create a pull request
• write a meaningful pr message that contains what happened in the pull request
• ask for a review from your colleagues
• after review merge into main
• move this issue in the board from In Progress tab into Done tab
• close this issue