Support "Maximum Number of Events" restriction for Favourites competitions

[JonEsparaz]

Is your feature request related to a problem? Please describe. For Favourites competitions (or Favorites is you're from the U.S.), organizers need to manually restrict the number of events a competitor registers for.

Examples:

• https://www.worldcubeassociation.org/competitions/OshawaFavourites2022
• https://www.worldcubeassociation.org/competitions/SnoCoFavorites2022
• https://www.worldcubeassociation.org/competitions/SacCubingXI2022

The website should be able to do this automatically.

Describe the solution you'd like

• When you have the "I would like to restrict competitors from registering for specific combinations of events" checkbox selected, there should be a field that allows you to restrict the maximum number of events a competitor may register for (let's call this M).
• The value M must be an integer between 1 and N-1 where N is the total number of events at the competition.
• When a competitor has more than M events selected, restrict them from registering for the competition (this should apply to the competitor's initial registration and updates to a registration either by the competitor or the organizers).
  • On the frontend, we can leverage the existing error state, but update for a maximum number of events allowed:

Additional context The implementation might have some similarity to https://github.com/thewca/worldcubeassociation.org/issues/7059 since we're enforcing an integer-based restriction on registrations.