[FEATURE] Disable User Sign Up via 'Sign Up form'

[p-sims]

Is your feature request related to a problem? Please describe.
Currently if you create an instance of attendize, then anyone can start creating users, organisation, and registering people for events using that instances with know oversight from administrator(s). This is particularly true if you have offline payments enabled, or not setup payment connection. There are multiple reasons why you might want control over who can and can't register, create organisers, create events...

• Eventbright now charges for free events with over 25 participants, so those looking to do registration for free events might start free loading on your instance
• Ethics policies and No Platform policies would require approve creations of and possibility to revoke organisers

Describe the solution you'd like
Ability to remove 'sign up' button, so new users can only be invited.
Ability to require 'owner' (or admin if such a categories exists) approval for new 'organisers'

Describe alternatives you've considered
A work around might be to try and edit code to remove 'sign up' button. Prehaps removing or changing permission for 'resources/views/Public/LoginAndRegister/Signup.blade.php' file might break sign up, but probably not in a nice way....

Editing resources/views/Public/LoginAndRegister/Login.blade.php to comment out:
@if(Utils::isAttendize()) <div class="signup"> <span>@lang("User.dont_have_account_button", ["url"=> route('showSignup')])</span> </div> @endif

Additional context
I'm hosting attendize so an non-profit can host registration for free events without having to rely on paid 3rd party platforms.