**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_by_timespan.return_value = [
            f"{source_prefix}/{file1}",
            f"{source_prefix}/{file2}",
        ]
        mock_proc = mock.MagicMock()
        mock_proc.returncode = 0
        mock_proc.stdout.readline = lambda: b""
        mock_proc.wait.return_value = None
        mock_popen = mock.MagicMock()
        mock_popen.return_value.__enter__.return_value = mock_proc
        mock_subprocess.Popen = mock_popen
        mock_subprocess.PIPE = "pipe"
        mock_subprocess.STDOUT = "stdout"
        op = GCSTimeSpanFileTransformOperator(
            task_id=TASK_ID,
            source_bucket=source_bucket,
            source_prefix=source_prefix,
            source_gcp_conn_id=source_gcp_conn_id,
            destination_bucket=destination_bucket,
            destination_prefix=destination_prefix,
            destination_gcp_conn_id=destination_gcp_conn_id,
            transform_script=transform_script,
        )
        with mock.patch.object(Path, "glob") as path_glob:
            path_glob.return_value.__iter__.return_value = [
                Path(f"{destination}/{file1}"),
                Path(f"{destination}/{file2}"),
            ]
            op.execute(context=context)
        mock_hook.return_value.list_by_timespan.assert_called_once_with(