box.cfg() waits for a bootstrap leader if there are no upstreams #5077
Description
The supervised bootstrap strategy now allows to bootstrap a
single-instance replicaset in the same way as multi-instance one: run
box.cfg({bootstrap_strategy = 'supervised'}) and wait for the
box.ctl.make_bootstrap_leader(<...>) command.
Requested by @Totktonada in tarantool/tarantool@08c7ff1.