Fixed a backward compatibility issue for PQv0 (#18716)

Author: nshestakov

ydb/core/persqueue/read_balancer__balancing.cpp

@@ -552,6 +552,7 @@ std::unique_ptr<TEvPersQueue::TEvReleasePartition> TPartitionFamily::MakeEvRelea
     auto& r = res->Record;
 
     r.SetSession(Session->SessionName);
+    r.SetCount(1);
     r.SetTopic(Topic());
     r.SetPath(TopicPath());
     r.SetGeneration(TabletGeneration());

ydb/core/protos/pqconfig.proto

@@ -653,7 +653,7 @@ message TReleasePartition {
     optional uint64 Generation = 2;
     optional string Session = 3;
     optional string ClientId = 4;
-    reserved 5; // optional uint32 Count = 5;
+    optional uint32 Count = 5;
     optional NActorsProto.TActorId PipeClient = 6;
     optional uint32 Group = 7;
     optional string Path = 8;