Sorry you’re having trouble, its not always easy to bring a mysql cluster up after a full outage. The charm in general does not make an attempt to start up in this scenario as its not always safe to do so and needs someone to be able to make some decisions.
The link that you’ve pasted from the forum is for percona cluster, which is a bit different than the mysql-innodb-cluster charm that’s been deployed here. The official MySQL docs do have a bit more detail regarding how to recover a cluster. Its similar to what you are doing, but you may want to log into one of the units and use the mysql-shell in order to do the recovery manually.
You can get the password for connecting to your mysql instances by running:
juju run --unit mysql-innodb-cluster/0 -- leader-get cluster-password
You can then access the mysql-shell by logging into one of the units and running the
mysql-shell.mysqlsh command. I’ve included an example using the ip address for your mysql-innodb-cluster/0 unit (though it may change if you are using space bindings, etc):
> juju ssh mysql-innodb-cluster/0
ubuntu@juju-0ec1c5-foo-11:~$ sudo mysql-shell.mysqlsh
mysql-py> cluster = dba.get_cluster('jujuCluster')
Hope this helps a bit.