Use correct logger for user details configuration warning

[avsan]

Summary

Use the InitializeUserDetailsBeanManagerConfigurer logger category for
the user details configuration warning.

The warning tells users to configure the logging level for
InitializeUserDetailsBeanManagerConfigurer, but the logger is currently
created from the inner InitializeUserDetailsManagerConfigurer class.

As a result, the logger that emits the warning does not match the logger
category referenced by the warning message.

Changes

• Use InitializeUserDetailsBeanManagerConfigurer.class when creating
  the logger.
• Add regression coverage verifying that the warning is emitted using
  the documented logger category.

Testing

• Added a regression test that failed before the change because the
  warning was emitted from the inner configurer logger.
• The regression test passes after the fix.
• AuthenticationConfigurationTests passes.
• :spring-security-config:checkFormat passes.
• git diff --check is clean.

Closes gh-19595