Fix apache#11323: Return list of gcs uris from LocalFilesystemToGCSOperator

[mlauter]

Relates to #11323

Updates the LocalFilesystemToGCSOperator to return the list of GCS uris of uploaded files.

This provider previously returned None, so this should be a safe change.

Testing

Updated and ran unit tests

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[shahar1]

Unfortunately you have been preceded by
#61355, whose author had also asked to be assigned first.
Please note for the next time :)