k/group: lower log error sev to DEBUG for errc::shutting_down

Reason for condition is legit and the tombstones will be replicated
the next time nodes start, so lowering log message severity to WARN.
Error text is logged for other error codes

(cherry picked from commit afccf5d)

src/v/kafka/server/group.cc

@@ -2806,11 +2806,17 @@ group::remove_topic_partitions(const std::vector<model::topic_partition>& tps) {
               "Replicated group cleanup record {} at offset {}",
               _id,
               result.value().last_offset);
+        } else if (result.error() == raft::errc::shutting_down) {
+            vlog(
+              klog.debug,
+              "Cannot replicate group {} cleanup records due to shutdown",
+              _id);
         } else {
             vlog(
               klog.error,
-              "Error occured replicating group {} cleanup records {}",
+              "Error occured replicating group {} cleanup records {} ({})",
               _id,
+              result.error().message(),
               result.error());
         }
     } catch (const std::exception& e) {