Thymeleaf cannot evaluate SpEL expressions

[eleftherias]

After upgrading to Spring Boot 3, Thymeleaf cannot resolve #httpServletRequest or #httpSession.
It's not clear yet if this is a bug or a misconfiguration in the samples.

For this reason, many Spring Boot samples are disabled.
They should be re-enabled when this is fixed.

[rwinch]

The issue is that httpServletRequest and other expression utility objects are no longer available. We need to manually add them to the model using something like @ModelAttribute.

I'm going to update the samples to use @ModelAttribute and @ControllerAdvice to expose the necessary properties.