admin api: skip partition info in /brokers end point

fetching partition information via health report API is heavy and
brokers API doesn't really use it. This patch avoids fetching that
information.

(cherry picked from commit 0ecb2a4)

src/v/redpanda/admin_server.cc

@@ -849,6 +849,7 @@ fill_maintenance_status(const cluster::broker_state& b_state) {
 ss::future<std::vector<ss::httpd::broker_json::broker>>
 get_brokers(cluster::controller* const controller) {
     cluster::node_report_filter filter;
+    filter.include_partitions = cluster::include_partitions_info::no;
 
     return controller->get_health_monitor()
       .local()