Race condition in creating a ca file and creating service certificates

Experienced in easyrsa-21

https://paste.ubuntu.com/p/kJDWMmTGvQ/

There's a race condition between create_certificate_authority and create_server_certificate which results in there not being a CA file creating the server certificates.

Specifically, looks like create_certificate_authority aborted early because juju hadn't provided a public address yet: https://github.com/charmed-kubernetes/layer-easyrsa/blob/2f4ade054b861c41acc39ae7e24bd581f0c1cb13/reactive/easyrsa.py#L208-L214

create_server_cert needs to wait for that to succeed, but the @when gates don't cover it

The "Public address not available yet" condition is specific to certain clouds where this failure was encountered