TCF (0.11.0): gRPC батчинг

[maryiaLichko]

Product: TCF
Since: 0.11.0
Root document: https://www.tarantool.io/en/clustersfederation/doc/latest
SME: @ DifferentialOrange @ themilchenko

Dev MR: https://gitlab.corp.mail.ru/tarantool/tcf/clusters-federation/-/merge_requests/110

Now all messages from gateway to destination could be batched (accumulated on Gateway and sent as one batch after a timeout or receiving some number of messages).
New Gateway config fields are added:

gateway:
  batch_size: 10     # maximum batch size before sending it to destination
  batch_timeout: 100 # timeout between forced sending of a batch, ms