[replication] box.info.synchro.queue gets a new field "owner"

[TarantoolBot]

Add the new field to box.info.synchro.queue

Product: Tarantool
Since: 2.10.0-beta1
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_info/
https://www.tarantool.io/en/doc/latest/book/replication/repl_sync/
SME: @ sergepetrenko
Peer reviewer: @
Estimate [@xuniq]: 3pt

Details

box.info.synchro.queue receives a new field: owner. It's a replica
id of the instance owning the synchronous transaction queue.

Once some instance owns the queue, every other instance becomes
read-only. When the queue is unclaimed, e.g.
box.info.synchro.queue.owner is 0, everyone may be writeable, but
cannot create synchronous transactions.

In order to claim or re-claim the queue, you have to issue
box.ctl.promote() on the instance you wish to promote.

When elections are enabled, the instance issues box.ctl.promote()
automatically once it wins the elections, no additional actions are
required.
Requested by @sergepetrenko in tarantool/tarantool@362e9a6.

Definition of done

• Add box.ctl.demote() link to https://www.tarantool.io/en/doc/latest/book/replication/repl_sync/ if necessary

Depends on and blocked by: #2044

There's a doc gap for box.info submodule documentation https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_info/:
box.info.synchro is not described at all. First, it should be described in #2044 and then the new owner field description can be added there.

Connected to #2278