Allow early `box.ctl.make_bootstrap_leader()`

Dev issue: https://github.com/tarantool/tarantool/issues/10858

Since Tarantool 3.4.0 it is allowed to call
box.ctl.make_bootstrap_leader() before the first box.cfg() call to
mark the instance as a bootstrap leader.

It works if box.cfg({bootstrap_strategy = 'supervised'}) is set,
ignored otherwise.

So, the following code is now possible:

box.ctl.make_bootstrap_leader()
box.cfg({
    bootstrap_strategy = 'supervised',
})

In earlier Tarantool version a user has to call box.cfg() in a
separate fiber first and then call box.ctl.make_bootstrap_leader().

Also, earlier Tarantool versions do not allow to bootstrap a database
using the 'supervised' bootstrap strategy if there are no upstreams
configured (empty box.cfg.replication). It means that there were no
way to bootstrap the database without iproto listening port configured
(box.cfg.listen) except using another bootstrap strategy.

Now, the 'supervised' bootstrap strategy let a user a full control
over the replicaset bootstrapping process.

If several instances call box.ctl.make_bootstrap_leader() to
bootstrap the database, each bootstraps its own database and it leads to
a JOIN failure. With great power comes great responsibility!
Requested by @Totktonada in https://github.com/tarantool/tarantool/commit/99d6a44b55fa22eff72547b53e892510f0452ae9.

Start by locating the documentation for box.ctl.make_bootstrap_leader(), box.cfg(), and the supervised bootstrap_strategy. Update it to explain calling make_bootstrap_leader() before box.cfg(), bootstrapping with no upstreams, and the risk of multiple bootstrap leaders; done means these behaviors and responsibilities are documented clearly.