https traffic to tempo is silently broken if traefik is not related to a certificates provider

[PietroPasotti]

Bug Description

if tempo is related to a certificates provider and an ingress, but the ingress doesn't have a certificate relation, tempo should set blocked so the user knows something is wrong. This helps address issues such as this one.

To Reproduce

see canonical/tempo-k8s-operator#153

Environment

any

Relevant log output

n/a

Additional context

possible ways to address this issue:
try to ping traefik with https and, on failure, we know the ingress isn't ready tot talk https and therefore all tracing relations are bork

[michaeldmitry]

Add a pebble service to fire a notice to check if the endpoint is up (can be part of the lib)