Charm logging

[PietroPasotti]

charm instrumentation library using loki push api to forward charm logs (same logs that go to the juju debug-log) to a loki instance.

Similar to what tempo's charm_tracing does, the library assumes the presence of a loki_push_api integration (that the charm might be using already to push workload logs).

This library exposes a decorator the user will put in front of a charm class.
The user will pass to the decorator the name of a charm method that returns a list of loki endpoint urls to which the charm logs should be forwarded. Presumably, the user will get those endpoints from LokiPushApiConsumer (but in practice we don't care how the url is obtained).

[sed-i]

Would you mind updating the PR description with the mechanism? Just guessing:

• User needs to pass a logging.getLogger instance so this lib could tag a long
• The lib relies on the loki_push_api relation schema to obtain loki server url
• User adds a class level decorator to the charm, utilizing some ops stuff