FEATURE: Add group settngs to allow users to leave a group freely.

https://meta.discourse.org/t/split-join-leave-freely-setting-on-groups/65565

spec/fabricators/group_fabricator.rb

@@ -1,3 +1,8 @@
 Fabricator(:group) do
   name { sequence(:name) { |n| "my_group_#{n}" } }
 end
+
+Fabricator(:public_group, from: :group) do
+  public_admission true
+  public_exit true
+end