Fix links to Spring Security Reference Guide in Accessing the H2 Console in a Secured Application

[hpoettker]

Thanks for merging #29932! Configuring Spring Security can be a challenge for beginners, and I think the added paragraph will be helpful.

I checked the deployed snapshot versions of the documentation. Unfortunately, only the 2.5.x version has working links to the Spring Security reference guide. For Spring Boot 2.6.x, they need to be adjusted against the new structure of the Spring Security documentation that came with 5.6: https://docs.spring.io/spring-boot/docs/2.6.5-SNAPSHOT/reference/htmlsingle/#data.sql.h2-web-console.spring-security

This PR is only half the solution, as {spring-security-docs} resolves to https://docs.spring.io/spring-security/reference/5.6.2. But all links with this particular version do not work while they do e.g. for 5.6.1 or 5.6. It seem to be the same problem as in #28407 but the fix for that has been basically reverted for #28618. As I don't know, what the best approach for this problem is, the PR doesn't address this.

[wilkinsona]

Thanks, @hpoettker. The docs should be available at https://docs.spring.io/spring-security/reference/5.6.2. I've asked the Security team to take a look.

[wilkinsona]

Thanks to @eleftherias, the 5.6.2 docs are now in place so we can merge this as-is I believe.

[wilkinsona]

Thanks very much, @hpoettker.