title: Make @ConfigurationProperties properties partially mandatory
body: <p>Given the following simple (not nested) configuration properties class:</p>
  
  <pre><code>@ConfigurationProperties("env")
  public class MyServiceProperties {
    private String anyProperty;
    private Boolean anyOther;
  ...
  </code></pre>
  
  <p>}</p>
  
  <p>How can I make sure that <em>anyProperty</em> is mandatory, i.e. env.any-property must be set to startup the application? Is there any difference for <em>nested configuration property classes</em>?</p>