types: Add default_group_name field to GroupPermissionSetting type.

This commit adds default_group_name field to GroupPermissionSetting
type which will be used to store the name of the default group for
that setting which would in most cases be one of the role-based
system groups. This will be helpful when we would have multiple
settings and we would need to set the defaults while creating
realm and streams.

zerver/lib/types.py

@@ -280,3 +280,4 @@ class GroupPermissionSetting:
     allow_internet_group: bool
     allow_owners_group: bool
     allow_nobody_group: bool
+    default_group_name: str

zerver/models.py

@@ -2643,6 +2643,7 @@ class Stream(models.Model):
             allow_internet_group=False,
             allow_owners_group=False,
             allow_nobody_group=False,
+            default_group_name=UserGroup.ADMINISTRATORS_GROUP_NAME,
         ),
     }
 

zerver/views/streams.py

@@ -591,8 +591,13 @@ def add_subscriptions_backend(
             allow_nobody_group=False,
         )
     else:
+        can_remove_subscribers_group_default = Stream.stream_permission_group_settings[
+            "can_remove_subscribers_group"
+        ].default_group_name
         can_remove_subscribers_group = UserGroup.objects.get(
-            name="@role:administrators", realm=user_profile.realm, is_system_group=True
+            name=can_remove_subscribers_group_default,
+            realm=user_profile.realm,
+            is_system_group=True,
         )
 
     for stream_dict in streams_raw: