Document non Servlet code separately

[xenoterracide]

The main reference documentation has a servlet section https://docs.spring.io/spring-security/reference/servlet/index.html, however if you are building code that does not need servlet access or cannot access servlet applications such as quartz, some unit tests, cli applications, event handlers (e.g. rabbitmq), etc, the documentation for this is hidden or mixed in in a way that is hard to find and understand. A new section that explicitly documents using spring security in these contexts would be especially helpful.

[dmkavanagh]

I would like to take this on.