[CV] Change replicas from 2 to 1 in swap-rebalance

Description

Change the no of. replicas from 2 to 1 in the swap-rebalance.

What's the problem?

The nodes are under-specced, which results in perpetual auto-compaction and perhaps various other unknown factors results in hitting hard out-of-memory errors in KV which seems to slow/stop the progress of the rebalance.

Seems to affect both mad-hatter and cheshire-cat so it's not a regression.

What's the fix?

Reduce the number of replicas from 2 to 1 to make the process of compaction easier allowing the rebalance to make progress.