new `replication.linearizable_quorum` option

[TarantoolBot]

A number of replicas to synchronize with before performing linearizable
transaction.

Linearizable transactions guarantee that if a write operation completes
before a read operation begins, then this read will always observe the
effects of that write. To ensure this, the node executing a linearizable
transaction must obtain information from enough remote peers to
determine the most up-to-date state of the replica set. That number of
peers can be configured with this option.

By default, the linearizable quorum is evaluated dynamically as
N - Q + 1, where: N – the current number of registered replicas in
the replica set, Q – the current value of replication.synchro_quorum.

This default guarantees quorum intersection between synchronous writes and
linearizable reads (R + Q = N + 1), which is a fundamental requirement
for linearizability.

Note:
To begin a linearizable transaction, the MVCC must be enabled and
txn_isolation must be set to linearizable, the transaction can only
perform requests to synchronous, local or temporary spaces.
Requested by @Serpentian in tarantool/tarantool@123e40f.