Support IPROTO_IS_SYNC

[oleg-jukovec]

The Tarantool 3.0 allows to enforce transaction to be synchronous. We could support the feature.

See:

1. Please add possiblity to set is_sync=true in box.begin to enforce transaction to be synchronous tarantool#8650
2. https://github.com/tarantool/tarantool/blob/03c184d4da9be9e1431762989833a6762a704cfb/src/box/iproto_constants.h#L218-L221