Improve deprecation notice in WebSecurityConfigurerAdapter

[marcusdacoregio]

The WebSecurityConfigurerAdapter has been deprecated and its javadoc is too hard to understand how to replace it.

We should be clearer on how to publish a SecurityFilterChain bean and WebSecurityCustomizer, and consider linking to the blog post https://spring.io/blog/2022/02/21/spring-security-without-the-websecurityconfigureradapter