notify the user when TLS is misconfigured

[PietroPasotti]

Enhancement Proposal

if you have traefik and prometheus, you should relate both with a certificates provider for tls to work.
if you only relate one of the two to certificates, traefik should notice and pop a warning/set blocked.

canonical/tempo-coordinator-k8s-operator#47

[dstathis]

This does not actually break anything, it's just probably wrong right?

[dstathis]

Actually I do not think we want this. It is a completely normal use case for traffic to terminate TLS and so prometheus does not need to.

The case where prometheus is related to TLS but traefik is not is admittedly more strange but I think we shouldn't really worry about it.

@PietroPasotti What do you think?