replication: prohibit roll back due to `replication_synchro_timeout`

Summary

• replication: prohibit roll back due to replication_synchro_timeout

To better match the canonical Raft design, this patch prohibits automatic transaction rollback due to replication.synchro_timeout. A new compat option has been added for this purpose. The compat option is named compat.replication_synchro_timeout and is 'old' by default. When set to 'new', the replication.synchro_timeout option has slightly different semantics. With this semantics, transactions are no longer rolled back at this timeout, replication.synchro_timeout is used only to wait confirmation in promote/demote and gc-checkpointing. If some transaction in limbo did not have time to commit within replication_synchro_timeput, the corresponding operation: promote/demote or gc-checkpointing can be aborted automatically (in this aspect, the behavior of the option is no different from what it was before). If 'old' is set, the option has the same semantics as before.

In order to be able to understand from the code what value the compat.replication_synchro_timeout option is set to - 'old' or 'new', a special Boolean tweak replication_synchro_timeout_enabled was introduced.

Note that PROMOTE and DEMOTE can still rollback a transaction. Only the ability to rollback by timeout has been prohibited.

Closes #7486

@TarantoolBot document Title: new compat option: 'compat.replication_synchro_timeout' Product: Tarantool Since: 3.3

Root document: New page - https://www.tarantool.io/en/doc/latest/reference/reference_lua/compat/replication_synchro_timeout/

The compat module allows you to choose between:

• the old behavior: unconfirmed synchronous transactions are rolled back after a replication.synchro_timeout.
• and the new behavior: A synchronous transaction can remain in the synchro queue indefinitely until it reaches a quorum of confirmations. replication.synchro_timeout is used only to wait confirmation in promote/demote and gc-checkpointing. If some transaction in limbo did not have time to commit within replication_synchro_timeput, the corresponding operation: promote/demote or gc-checkpointing can be aborted automatically.

Close #... Docs follow-up: not necessary / new issue

Ref #73 (closed)