k/connection_context: use warn severity for unsupported api versions

When client requests an unsupported API version it is not an unexpected
situation and should not be logged with ERROR severity. Introduced
separate exception handler for unsupported API version exceptions.

Fixes: redpanda-data#5868

Signed-off-by: Michal Maslanka <michal@redpanda.com>

src/v/kafka/server/connection_context.cc

@@ -72,6 +72,14 @@ ss::future<> connection_context::process_one_request() {
                       return ss::make_ready_future<>();
                   }
                   return dispatch_method_once(std::move(h.value()), s)
+                  .handle_exception_type(
+                    [this](const kafka_api_version_not_supported_exception& e) {
+                        vlog(
+                          klog.warn,
+                          "Unsupported API version in request from {} - {}",
+                          _rs.conn->addr,
+                          e.what());
+                    })
                     .handle_exception_type([this](const std::bad_alloc&) {
                         // In general, dispatch_method_once does not throw,
                         // but bad_allocs are an exception.  Log it cleanly