**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}`

num_max_attempts,
                        )
                        raise e
                    
                    timeout_seconds = 1.0 * 2 ** (num_file_attempts - 1)
                    time.sleep(timeout_seconds)
                    continue
        client = self.get_conn()
        bucket = client.bucket(bucket_name)
        blob = bucket.blob(blob_name=object_name, chunk_size=chunk_size)
        if metadata:
            blob.metadata = metadata
        if filename and data:
            raise ValueError(
                "'filename' and 'data' parameter provided. Please "
                "specify a single parameter, either 'filename' for "
                "local file uploads or 'data' for file content uploads."
            )
        elif filename:
            if not mime_type:
                mime_type = "application/octet-stream"
            if gzip:
                filename_gz = filename + ".gz"
                with open(filename, "rb") as f_in:
                    with gz.open(filename_gz, "wb") as f_out:
                        shutil.copyfileobj(f_in, f_out)
                        filename = filename_gz
            _call_with_retry(
                partial(blob.upload_from_filename, filename=filename, content_type=mime_type, timeout=timeout)
            )