RATIS-2393 Add Span Context to RaftRpcMessage Proto

Author: taklwu

ratis-proto/src/main/proto/Raft.proto

@@ -121,6 +121,7 @@ message RaftRpcRequestProto {
   uint64 timeoutMs = 13;
   RoutingTableProto routingTable = 14;
   SlidingWindowEntry slidingWindowEntry = 15;
+  SpanContextProto spanContext = 16;
 }
 
 message SlidingWindowEntry {
@@ -569,3 +570,8 @@ message LogInfoProto {
   TermIndexProto committed = 3;
   TermIndexProto lastEntry = 4;
 }
+
+// The attribute map for opentelemetry trace
+message SpanContextProto {
+  map<string, string> context = 1;
+}