CsrfDsl does not have a spa() configuration method.

Describe the bug
According to the documentation, org.springframework.security.config.annotation.web.CsrfDsl should have a spa() configuration method, but it doesn't.
https://docs.spring.io/spring-security/reference/servlet/exploits/csrf.html#csrf-integration-javascript-spa

To Reproduce

    @Bean
    open fun securityFilterChain(http: HttpSecurity): SecurityFilterChain {
        http {
            // ...
            csrf {
                spa()
            }
        }
        return http.build()
    }

Expected behavior
According to the documentation, CsrfDsl should have a spa() configuration method.

Start by reading the CsrfDsl API and the linked CSRF SPA documentation section, then reproduce the Kotlin securityFilterChain example from the issue. Confirm whether the documented spa() configuration is missing from the DSL or the documentation; done means the example and the available API agree and are covered by the relevant project tests.