This commit introduced 'creator' and 'date_created'
fields in user groups, allowing users to view who
created the groups and when.
Both fields can be null for groups without creator data.
This commit adds a new group level setting can_manage_group
for configuring who can manage a group. This commit only adds
the field in database and make changes to automatically create
single user groups corresponsing to acting user
which will be the default value for this setting.
Fixes part of #25928.
This commit removes name, description, is_system_group and
can_mention_group fields from UserGroup model and rename
them in NamedUserGroup model.
Fixes#29554.
