Add explicit anchor to discussion about constructor VS. setter injection

This commit adds an Asciidoc anchor to the section on different injection
styles to be able to link to the discussion as official recommendation.

Closes gh-1681

src/docs/asciidoc/core/core-beans.adoc

@@ -1020,6 +1020,7 @@ definitions, annotated components (i.e., classes annotated with `@Component`,
 sources are then converted internally into instances of `BeanDefinition` and used to
 load an entire Spring IoC container instance.
 
+[[beans-constructor-vs-setter-injection]]
 .Constructor-based or setter-based DI?
 ****
 Since you can mix constructor-based and setter-based DI, it is a good rule of thumb to