Remove logback-access from the core framework

[zUniQueX]

As mentioned in this comment we could/should think of dropping support for logback-access. Logback doesn't support Jetty 12 yet and the related issue hasn't received comments for about two months.

This PR is meant to show the consequences of removing the logback-access dependency from the core framework modules.
The LogbackAccessRequestLogFactory will be removed and LogbackClassicRequestLogFactory will be the new default.

The JSON logging related access-json layout will be removed too.

I've further evaluated what it would look like supporting logback-access without the hard dependency in dropwizard-request-logging and dropwizard-json-logging. We currently have a workaround to get the LogbackAccessRequestLog working again, so we could lower the migration costs with supporting the workaround for some time (then preferably in a separate repo which will be deprecated directly). A necessary precondition for that is introducing the ServerCustomizer interface to allow customizations of the Jetty handler chain.

[zUniQueX]

@dropwizard/committers I've come back to this one and don't have a strong opinion on distributing the separate artifact or not. Personally, I don't like introducing the ServerCustomizer.

Feel free to share your opinions, I'll update the PR accordingly.

[zUniQueX]

@dropwizard/committers The logback team recently pushed a release of logback-access with Jetty 12 compatibility in a new repo. Shall I close this PR if we get further updates or should we move away from logback-access anyway?