Allow to configure retry policy on a per-task basis // add javadoc

transactionoutbox-core/src/main/java/com/gruelbox/transactionoutbox/RetryPolicyAware.java

@@ -2,8 +2,30 @@
 
 import java.time.Duration;
 
+/**
+ * Defines a custom retry policy for tasks scheduled in the {@link TransactionOutbox}.
+ * <p>
+ * Implement this interface in the class that is passed to
+ * {@link TransactionOutbox#schedule(Class)} to override the default retry behavior.
+ * </p>
+ */
 public interface RetryPolicyAware {
+  /**
+   * Determines the wait duration before retrying a failed task.
+   *
+   * @param attempt   The current retry attempt (starting from 1).
+   * @param throwable The exception that caused the failure.
+   * @return The duration to wait before the next retry.
+   */
   Duration waitDuration(int attempt, Throwable throwable);
 
+  /**
+   * Specifies the maximum number of retry attempts before blocking the task.
+   *
+   * @param attempt   The current retry attempt (starting from 1).
+   * @param throwable The exception that caused the failure.
+   * @return The number of attempts after which the task should be blocked.
+   * If the returned value is less than or equal to {@code attempt}, the task is blocked immediately.
+   */
   int blockAfterAttempts(int attempt, Throwable throwable);
 }