Add key-value metadata fields

dnsmessage.proto

@@ -96,6 +96,17 @@ message PBDNSMessage {
   optional string deviceName = 19;              // Device name of the requestor
   optional uint32 fromPort = 20;                // Source port of the DNS query (client)
   optional uint32 toPort = 21;                  // Destination port of the DNS query (server)
+
+  message MetaValue {
+    repeated string stringVal = 1;
+    repeated int64 intVal = 2;
+  }
+
+  message Meta {
+    required string key = 1;                    // MUST be unique, so if you have multiple values they must be aggregated into on Meta
+    required MetaValue value = 2;
+  }
+  repeated Meta meta = 22;                      // Arbitrary meta-data - to be used in future rather than adding new fields all the time
 }
 
 message PBDNSMessageList {