Review logger for OTel components to use json format for agent logs

[aengusrooneygrafana]

When I apply a json format to the agent logs, I get one (annoying) line, that is not json format from OTEL logger -

{"agent":"prometheus","caller":"node.go:85","component":"cluster","level":"info","msg":"applying config","ts":"2022-01-12T15:09:14.625104Z"}
{"agent":"prometheus","caller":"remote.go:180","component":"cluster","level":"info","msg":"not watching the KV, none set","ts":"2022-01-12T15:09:14.625223Z"}
ts=2022-01-12T15:09:14Z level=info caller=traces/traces.go:123 msg="Traces Logger Initialized" component=traces
{"caller":"node_exporter.go:49","integration":"node_exporter","level":"info","msg":"Enabled node_exporter collectors","ts":"2022-01-12T15:09:14.626348Z"} 

We use zap as logger for OTel components, so it should be simple to use a specific formatting (JSON in this case). We instantiate the logger in here https://github.com/grafana/agent/blob/main/pkg/traces/traces.go#L112-L126

[aengusrooneygrafana]

@mapno for info - https://raintank-corp.slack.com/archives/CSN5HV0CQ/p1642000857040500