Allow composing @Retryable annotation with @AliasFor recover method

[gmedici]

Creating a custom annotation composing @Retryable will not get the actual recover argument value even when the recover method is annotated with @AliasFor. Eg:

@Target({ ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Retryable(maxAttempts = 4)
public @interface ComposedRetryable {
    @AliasFor(annotation = Retryable.class, attribute = "recover")
    String recover() default "";
}

The reason is that RecoverAnnotationRecoveryHandler is still using AnnotationUtils.findAnnotation() instead of AnnotatedElementUtils.findMergedAnnotation()

[artembilan]

It also would be great if you add some explanation and sample for this feature in the README of the project: https://github.com/spring-projects/spring-retry#declarative-retry.

Thank you!

[artembilan]

... and back-ported to 1.3.x as 2e7a73c after some minor conflict resolution.

@gmedici ,

thank you very much for contribution; looking forward for more!