KafkaSinkCluster: route DescribeGroups request

[rukai]

yet another split message type. It follows the same logic as DeleteGroups message type where we route and split by group id.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #1816 will not alter performance

_{Comparing rukai:describe_groups (fc70d86) with main (cb8cf1b)}

Summary

✅ 38 untouched benchmarks