**Description**

Support passing multiple prefixes to `GoogleCloudStorageListOperator` and `GoogleCloudStorageDeleteOperator` operators.

**Use case / motivation**

I have this folder structure in GCS bucket.

```
+-- year={year}
|   +-- month={month}
|       +--day={day}
|           +-- topic={topic1}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic2}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic3}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic4}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic5}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic6}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic7}
|       +--day={day}
|           +-- topic={topic1}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic2}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic3}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic4}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic5}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic6}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           +-- topic={topic7}
|                 +--file 1
|                 +--file 2
|                 +--file 3
|           ....
```

What I need to achieve is delete one day of objects. For example, I need to delete objects in `year=2020/month=08/day=19`. I can do that easily using `gsutils`. In `gsutil` you can delete them via wild card `gsutil ear=2020/month=08/day=19/*` but using the REST APIs you can't even if you use a prefix. The reason is there is no one prefix to get all the objects inside a folder. I achieved that by using multiple prefixes and for each prefix, I will get the list of objects. Unfortunately, I can't pass more than one prefix to the operators.

**Prefixes used**
- `year=2020/month=08/day=19/topic={topic1}`
- `year=2020/month=08/day=19/topic={topic2}`
- `year=2020/month=08/day=19/topic={topic3}`
- `year=2020/month=08/day=19/topic={topic4}`
- `year=2020/month=08/day=19/topic={topic5}`
- `year=2020/month=08/day=19/topic={topic6}`
- `year=2020/month=08/day=19/topic={topic7}`

mock_hook.return_value.list.return_value = MOCK_FILES
        operator = GCSListObjectsOperator(
            task_id=TASK_ID, bucket=TEST_BUCKET, prefix=PREFIX, delimiter=DELIMITER
        )
        files = operator.execute(context=mock.MagicMock())
        mock_hook.return_value.list.assert_called_once_with(
            bucket_name=TEST_BUCKET, prefix=PREFIX, delimiter=DELIMITER
        )
        assert sorted(files) == sorted(MOCK_FILES)
class TestGCSFileTransformOperator:
    @mock.patch("airflow.providers.google.cloud.operators.gcs.NamedTemporaryFile")
    @mock.patch("airflow.providers.google.cloud.operators.gcs.subprocess")
    @mock.patch("airflow.providers.google.cloud.operators.gcs.GCSHook")
    def test_execute(self, mock_hook, mock_subprocess, mock_tempfile):
        source_bucket = TEST_BUCKET
        source_object = "test.txt"
        destination_bucket = TEST_BUCKET + "-dest"
        destination_object = "transformed_test.txt"
        transform_script = "script.py"
        source = "source"
        destination = "destination"
        
        mock1 = mock.Mock()
        mock2 = mock.Mock()
        mock1.name = source
        mock2.name = destination
        mock_tempfile.return_value.__enter__.side_effect = [mock1, mock2]
        mock_proc = mock.MagicMock()
        mock_proc.returncode = 0
        mock_proc.stdout.readline = lambda: b""