fix(tracing): Don't throw error logs in valid scenarios

[mmkay]

Issue

While analyzing canonical/grafana-agent-operator#219 with @michaeldmitry in the context of the k8s charm, we realized some of the logs might be misleading. If the tracing provider cannot (yet) serve any of the requested protocols, the expected outcome would be to return an empty list. Tracing consumer will then throw an error log the charm operator cannot do anything about.

Also we noticed we have an inconsistency in the behaviour when more than 1 receiver of the same protocol would be returned: the log says we're returning the first entry, the actual behaviour is that we exit early.

Solution

Reduce the logs severity and allow to return the first matching receiver.

Context

Testing Instructions

Upgrade Notes