Implement the directory_list() function inside the storage source class for GCP. The function should list all the files in the bucket using the connection class. The function should be calling the connection classes listObject() function. This ticket also implements the file_exists() function inside the file system class for GCP. The function should use the connection class to check if the file exists or not. Once implemented the developer will also need to test this functionality through python.

Definition of Done
The directory_list() and file_exists() function works in the storage source class and python test should be testing this functionality.