Add JavaDoc

Author: qzchenwl

src/main/java/org/dataloader/CacheKey.java

@@ -36,6 +36,15 @@ public interface CacheKey<K> {
      */
     Object getKey(K input);
 
+    /**
+     * Returns the cache key that is created from the provided input key and context.
+     *
+     * @param input the input key
+     *
+     * @param context the context
+     *
+     * @return the cache key
+     */
     default Object getKeyWithContext(K input, Object context) {
         return getKey(input);
     }