Include time spend in authentication in request log

The request logging is currently triggered by a servlet filter. Filters run after authentication and therefore the time spent in authentication is not included. In addition time spent in anything before authentication (like preprocessors) is not included either.
We should change RequestLoggerFilter from a filter to an early running Preprocessor. However,currently the RequestLoggerFilter has two purposes - one is the logging and the other one is preparing request and response objects. We need to split that functionality and keep it in the filter - Preprocessors run for every http context, not just Sling so we need to avoid that this code runs outside of Sling's context.