Enable MultiField annotation on entity getter.

Original Pull Request #2649
Closes #2600

Author: sothawo

Diff for: src/main/java/org/springframework/data/elasticsearch/annotations/MultiField.java

@@ -30,7 +30,7 @@
  * @author Peter-Josef Meisch
  */
 @Retention(RetentionPolicy.RUNTIME)
-@Target({ ElementType.FIELD, ElementType.ANNOTATION_TYPE })
+@Target({ ElementType.FIELD, ElementType.ANNOTATION_TYPE, ElementType.METHOD })
 @Documented
 public @interface MultiField {