Automatic data rebalancing

[rkruze]

When a user adds a node or deletes a topic, data should be automatically rebalanced across the cluster.

[vsaraswat]

Per our discussion this is aimed for 22.1.1 -- @dotnwat @dswang looks like 22.1.1 milestone is empty so feel free to assign to which Q1FY23 category makes sense

[scallister]

It might be worth doing periodic balancing at some interval in addition to the above cases.

For example in this instance rebalancing could be helpful because the orange node has more disk usage than the dark blue node. In this instance orange is also receiving more bytes/second than blue.

It would also be helpful if there were a REST endpoint (and/or rpk command) to trigger a rebalance manually.

[dotnwat]

@ztlpn is on the case!