added group_fail_limits and skip_unspecified_group_on_failure;
- The `group_fail_limits` option allows you to specify the maximum number of failed tasks for a group before the runner skips the rest of the waiting tasks in a group.
- The `skip_unspecified_group_on_failure` option sets the fail limit to 1 for all groups which do not have a `group_fail_limit` specified.