Config option tls-ca is always required, even when tls-cert is signed by a trusted 3rd party CA

[przemeklal]

Bug Description

I tried setting tls-cert and tls-key only as the cert is signed by a well-trusted 3rd party CA. I ended up with Traefik in the blocked state Please set tls-cert, tls-key, and tls-ca.

I don't think it makes sense to block the charm because of the missing CA cert option when it might be signed by a trusted 3rd party authority and there's no need to provide that CA separately.

For what it's worth, the described desired behaviour is how it works in e.g. openstack charms - their equivalent of the tls-ca config option (ssl_ca) is totally optional.

To Reproduce

Deploy traefik, set only to tls-cert and tls-key, and leave tls-ca empty.

Environment

Traefik charm rev 180

Relevant log output

n/a

Additional context

No response