**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}`

if gzip:
                os.remove(filename)
            self.log.info("File %s uploaded to %s in %s bucket", filename, object_name, bucket_name)
        elif data:
            if not mime_type:
                mime_type = "text/plain"
            if gzip:
                if isinstance(data, str):
                    data = bytes(data, encoding)
                out = BytesIO()
                with gz.GzipFile(fileobj=out, mode="w") as f:
                    f.write(data)
                data = out.getvalue()
            _call_with_retry(partial(blob.upload_from_string, data, content_type=mime_type, timeout=timeout))
            self.log.info("Data stream uploaded to %s in %s bucket", object_name, bucket_name)
        else:
            raise ValueError("'filename' and 'data' parameter missing. One is required to upload to gcs.")
    def exists(self, bucket_name: str, object_name: str, retry: Retry = DEFAULT_RETRY) -> bool:
        """
        Checks for the existence of a file in Google Cloud Storage.
        :param bucket_name: The Google Cloud Storage bucket where the object is.
        :param object_name: The name of the blob_name to check in the Google cloud
            storage bucket.
        :param retry: (Optional) How to retry the RPC
        """
        client = self.get_conn()
        bucket = client.bucket(bucket_name)
        blob = bucket.blob(blob_name=object_name)
        return blob.exists(retry=retry)
    def get_blob_update_time(self, bucket_name: str, object_name: str):