feat: add labels to NodeInfo

include/NodeInfo.h

@@ -3,6 +3,7 @@
 #include <IPAddress.h>
 #include <vector>
 #include <tuple>
+#include <map>
 
 struct NodeInfo {
     String hostname;
@@ -18,6 +19,7 @@ struct NodeInfo {
     } resources;
     unsigned long latency = 0; // ms since lastSeen
     std::vector<std::tuple<String, int>> apiEndpoints; // List of registered endpoints
+    std::map<String, String> labels; // Arbitrary node labels (key -> value)
 };
 
 const char* statusToStr(NodeInfo::Status status);