Add a logging infrastructure

Add a logging infrastructure as defined in ADR 0003.

It should be possible to configure the logging from the playbook. All user messages should be funneled through this logger.

The scope of this issue is to introduce a configurable logging infrastructure (i.e., a logger) into Antora and also to route Asciidoctor messages into that logger. What's not in scope is to add additional log messages (except where needed to be able to test the functionality). Adding additional log messages should be handled in a separate issue. In other words, we want to get the messages we already have coming from the application managed and under control.