Additional features for the admin page about the upper-bound limit on competitions submissions

[OhMaley]

This ticket lists all feature we want to add to the PR https://github.com/codalab/codalab-competitions/pull/3163 after it is merged.

• Move the default limit into the settings (so it can be easily configurable)
• Display the limit at the top of the admin page
• In the table add columns for
  • the effective limit
  • organizer email
  • competition link
  • button to force the effective limit to be equal to the maximum limit that the admin has set
  • Fix the redirection page
• Make the table sortable
• Create a wiki page about this view and add a question mark button somewhere on the admin page