Rebalancing without topic configuration files

[petedannemann]

One of the best features of topicctl is its topic rebalancing capabilities. It would be ideal for this to not require the topic configuration files as that would allow users to user topicctl to rebalance their clusters while still utilizing other tools for topic management, like the kafka-terraform-provider. A workaround right now is to first run the bootstrap step to generate the configs and follow that up with rebalance. Adding a flag to the rebalance command to avoid the intermediate configuration files and rebalance the topics without them would be a big improvement for this use case.