Fix link in the In-Memory Authentication documentation

[lukasdo]

For details see #14688

[marcusdacoregio]

Hi, @lukasdo. Can you please squash your commits in preparation for merge?

[marcusdacoregio]

@lukasdo, are you sure that the link you changed redirect to a page? I tested on my side and it returned Page Not Found. I believe that the link should redirect to https://docs.spring.io/spring-security/reference/servlet/authentication/passwords/input.html.

You can generate the documentation by following the steps in this guide.

[lukasdo]

@marcusdacoregio, I will check the documentation generation in a bit. However the link should be correct. I used the same link that is referenced on other pages e.g.: JDBC Authentication and LDAP Authentication

You are right in earlier working versions of the documentation the link seemed to be referencing the chapter Reading the Username & Password, although the section id should be leading to 10.10. Username/Password Authentication.
Additionally the DaoAuthenticationProvider page is referencing Reading the Username & Password in the text but linking to the Username/Password Authentication page.

Hope this is understandable...