Spring Add logging reference documentation [SPR-17626]

Sébastien Deleuze opened SPR-17626 and commented

Unless I missed something, I think we have no reference documentation for the logging infrastructure we provide in spring-jcl, only a mention in https://github.com/spring-projects/spring-framework/wiki/What%27s-New-in-Spring-Framework-5.x which says:

Spring Framework 5.0 comes with its own Commons Logging bridge out of the box: * spring-jcl instead of standard Commons Logging; still excludable/overridable. * Autodetecting Log4j 2.x, SLF4J, JUL (java.util.logging) without any extra bridges.

I think it would deserve a short paragraph in our reference documentation + a link to https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#boot-features-logging for concrete implementation and configuration.

Issue Links: - #8611 Logback support