GCSFileTransformOperator: New templated fields source_object, destination_object (#23328)

* `GCSFileTransformOperator`: New templated fields `source_object`, `destination_object`
* Add `source_object`, `destination_object` as templated fields
* fix docstring
closes: #23327

Author: eladkal

airflow/providers/google/cloud/operators/gcs.py

@@ -536,8 +536,12 @@ class GCSFileTransformOperator(BaseOperator):
     data from source, transform it and write the output to the local
     destination file.
 
-    :param source_bucket: The key to be retrieved from GCS. (templated)
-    :param destination_bucket: The key to be written from GCS. (templated)
+    :param source_bucket: The bucket to locate the source_object. (templated)
+    :param source_object: The key to be retrieved from GCS. (templated)
+    :param destination_bucket: The bucket to upload the key after transformation.
+        If not provided, source_bucket will be used. (templated)
+    :param destination_object: The key to be written in GCS.
+        If not provided, source_object will be used. (templated)
     :param transform_script: location of the executable transformation script or list of arguments
         passed to subprocess ex. `['python', 'script.py', 10]`. (templated)
     :param gcp_conn_id: The connection ID to use connecting to Google Cloud.
@@ -553,7 +557,9 @@ class GCSFileTransformOperator(BaseOperator):
 
     template_fields: Sequence[str] = (
         'source_bucket',
+        'source_object',
         'destination_bucket',
+        'destination_object',
         'transform_script',
         'impersonation_chain',
     )