registration: Collect organization type on sign-up.

zerver/forms.py

@@ -114,6 +114,7 @@ class RegistrationForm(forms.Form):
     # actually required for a realm
     password = forms.CharField(widget=forms.PasswordInput, max_length=MAX_PASSWORD_LENGTH)
     realm_subdomain = forms.CharField(max_length=Realm.MAX_REALM_SUBDOMAIN_LENGTH, required=False)
+    realm_type = forms.IntegerField(required=False)
 
     def __init__(self, *args: Any, **kwargs: Any) -> None:
         # Since the superclass doesn't except random extra kwargs, we