Discourse Connect can be used to manage group memberships of users by including a `add_groups`, `remove_groups` or `groups` attribute in the Discourse Connect payload. However, additions/deletions of users from groups aren't logged to the groups logs (available at `/g/<group>/manage/logs`) which can cause confusions to admins they try to figure out when/how users were added or removed from a group. This commit makes Discourse Connect add entries to the groups logs when it makes changes to users' group memberships.