**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}`

test_bucket = "test_bucket"
        test_object = "test_object"
        encoding = "utf-8"
        gzip_ctx = mock_gzip.return_value.__enter__.return_value
        data = mock_bytes_io.return_value.getvalue.return_value
        upload_method = mock_service.return_value.bucket.return_value.blob.return_value.upload_from_string
        self.gcs_hook.upload(test_bucket, test_object, data=testdata_string, gzip=True)
        byte_str = bytes(testdata_string, encoding)
        mock_gzip.assert_called_once_with(fileobj=mock_bytes_io.return_value, mode="w")
        gzip_ctx.write.assert_called_once_with(byte_str)
        upload_method.assert_called_once_with(data, content_type="text/plain", timeout=60)
    @mock.patch(GCS_STRING.format("BytesIO"))
    @mock.patch(GCS_STRING.format("gz.GzipFile"))
    @mock.patch(GCS_STRING.format("GCSHook.get_conn"))
    def test_upload_data_bytes_gzip(self, mock_service, mock_gzip, mock_bytes_io, testdata_bytes):
        test_bucket = "test_bucket"
        test_object = "test_object"
        gzip_ctx = mock_gzip.return_value.__enter__.return_value
        data = mock_bytes_io.return_value.getvalue.return_value
        upload_method = mock_service.return_value.bucket.return_value.blob.return_value.upload_from_string
        self.gcs_hook.upload(test_bucket, test_object, data=testdata_bytes, gzip=True)
        mock_gzip.assert_called_once_with(fileobj=mock_bytes_io.return_value, mode="w")
        gzip_ctx.write.assert_called_once_with(testdata_bytes)
        upload_method.assert_called_once_with(data, content_type="text/plain", timeout=60)
    @mock.patch(GCS_STRING.format("GCSHook.get_conn"))
    def test_upload_exceptions(self, mock_service, testdata_file, testdata_string):