Add a new `--keep-throttle` boolean flag to the apply command that allows
users to preserve replication throttle settings instead of having them
automatically removed after applying topic configurations.

This is particularly useful for topics where throttle settings
(leader.replication.throttled.replicas, follower.replication.throttled.replicas)
are intentionally configured in the topic YAML and should be maintained
across applies.

Due to the possibility of partition shuffling we need to apply the throttle config from the original topic definition file again in the end. During the partition shuffling step, the throttle settings will be overwritten per partition automatically and then deleted in the end, removing any wanted throttle settings from the configuration file or a previous set topic/broker throttle, those need to be restored.

Changes:
- Add --keep-throttle flag to apply command
- Skip automatic throttle removal when flag is set
- Update help documentation

Example usage:
  topicctl apply --keep-throttle --skip-confirm \
    --cluster-config cluster.yaml topics/my-topic.yaml