Added newcomers_allowed field and started adding to competition form

[dunkOnIT]

This is per the recent update to WCRP which allows organizers to specify having a WCA ID as a qualification criterion.

Note: I'm still going to add a conditional to the field in the competition form that it only shows is v2 registrations are enabled

2 things:

1. Implementing the field in the form - I've stumbled around with the React form, but am unsure how to get newcomersAllowed into this piece of code without throwing an error:

eventRestrictions: {
        newcomersAllowed,
        earlyPuzzleSubmission,
        qualificationResults,
        eventLimitation,
      },

2. Are we concerned at bloat in the competition model with the number of properties it has? I guess this isn't the place to address that, but I'm wondering if at some point we want to store the preferences separately from the "core" competition data - but that's a whole redesign project on its own.

And then there's a lot of nitting that could be done on "newcomer" vs "first-timer" vs "has a WCA ID", as well as where in the competition form this should be displayed.

[dunkOnIT]

• [ ] Make remark required
• [ ] usesV2Registrations not becoming true even when it should
• [x] Only show newcomer field if v2 registrations enabled