[#525] v2/container: Return session token and signature in Get

In recent API changes `GetResponseBody` carries session token and signature.
In recent API Go lib changes `Container` structure carries its session
token and signature.

Write session token and signature of container from sidechain to Get
response body in node's `ContainerService` server.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/container/morph/executor.go

@@ -65,6 +65,8 @@ func (s *morphExecutor) Get(ctx context.Context, body *container.GetRequestBody)
 
 	res := new(container.GetResponseBody)
 	res.SetContainer(cnr.ToV2())
+	res.SetSignature(cnr.Signature().ToV2())
+	res.SetSessionToken(cnr.SessionToken().ToV2())
 
 	return res, nil
 }