Make better use of the different log levels

Today almost everything that the agent logs is logged at the `debug` level. This means that it's either all or nothing if you want to know what's going on. This also makes it pretty impractical to get any information out of the agent in a production environment as it would spam the logs.

I therefore suggest that:

1. We change the current default log level to something higher (e.g. from `info` to `warn` or maybe even `error`)
1. We go over all places where we log anything and reevaluate their level

Example:

When the agent starts up it can output its current config. But only on the `debug` level. This would be useful for users to know in their production environment, but it wouldn't make sense to change the `logLevel` to `debug` just for that.