Add RateLimit to registrations (HyphaApp#3493)

A vulnerability was introduced with HyphaApp#3064 where registrations could be
created en masse using arbitrary email addresses. An attacker could use
this to make hypha auto generate mass emails to those recipients. Adding
a ratelimit to the registration should prevent that from being too
aggressive.

Co-authored-by: Frank Duncan <[email protected]>

hypha/apply/users/views.py

@@ -49,6 +49,7 @@
 
 User = get_user_model()
 
+@method_decorator(ratelimit(key='ip', rate=settings.DEFAULT_RATE_LIMIT, method='POST'), name='dispatch')
 class RegisterView(View):
     form = CustomUserCreationForm()