Migrate samples to UserDetailsManagerResourceFactoryBean

[philwebb]

See spring-projects/spring-security#4564 (comment)

We can do something like this:

@Bean
public InMemoryUserDetailsManager userDetailsManager() throws Exception {
    return UserDetailsManagerResourceFactoryBean.fromResource(new InMemoryResource("user=secret,USER")).getObject();
}

[philwebb]

Actually Rob has added a new method, we can now do:

@Bean
public InMemoryUserDetailsManager udm() {
    return new InMemoryUserDetailsManager(User.withUsername("user").password("secret").roles("USER").build());
}