Manage recurring challenges

[Tirodem]

Following #107 , #108 , #110

Process

When a challenge end date becomes a past date (check can be done daily), if "Monthly challenge" = true :
=> if this challenge has no recurring parent ID, use it's own ID as a recurring paren ID value
=> create a new challenge that is a copy of the finishing challenge

UI

When on /admin/challenge/{id} , if there's a recurring parent ID for this challenge, display a list of every challenge with the same recurring parent ID