issue: #41874
- Optimize balance_checker to support balancing multiple collections
simultaneously
- Add new parameters for segment and channel balancing batch sizes
- Add enableBalanceOnMultipleCollections parameter
- Update tests for balance checker
This change improves resource utilization by allowing the system to
balance multiple collections in a single trigger with configurable batch
sizes.
Signed-off-by: Wei Liu <wei.liu@zilliz.com>