Use created_at as the default sorting option for group lists

During the [rollout] of the explore_groups_vue feature flag. We've noticed a significant degradation on our API response time after we switched to using updated_at as the default sorting option.

To get around this, we need to migrate the group list pages to use created_at as the default sorting option.

This is due to the lack of database index on the updated_at column. This is being looked at separately in Improve performance when sorting namespaces by ... (#588691)