fix(doc): Add discriptions for TransactionCallable interface (#1644)

* fix(doc): Add discriptions for TransactionCallable interface

* chore: generate libraries at Mon Oct 28 22:49:19 UTC 2024

---------

Co-authored-by: cloud-java-bot <[email protected]>

Author: cindy-peng

google-cloud-datastore/src/main/java/com/google/cloud/datastore/Datastore.java

@@ -51,6 +51,13 @@ public interface Datastore extends Service<DatastoreOptions>, DatastoreReaderWri
    * @param <T> the type of the return value
    */
   interface TransactionCallable<T> {
+    /**
+     * Callback's invoke method for the TransactionCallable.
+     *
+     * @param readerWriter DatastoreReaderWriter associated with the new transaction
+     * @return T The transaction result
+     * @throws Exception upon failure
+     */
     T run(DatastoreReaderWriter readerWriter) throws Exception;
   }