**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"
        both_params_except = (
            "'filename' and 'data' parameter provided. Please "
            "specify a single parameter, either 'filename' for "
            "local file uploads or 'data' for file content uploads."
        )
        no_params_except = "'filename' and 'data' parameter missing. One is required to upload to gcs."
        with pytest.raises(ValueError, match=re.escape(no_params_except)):
            self.gcs_hook.upload(test_bucket, test_object)
        with pytest.raises(ValueError, match=re.escape(both_params_except)):
            self.gcs_hook.upload(test_bucket, test_object, filename=testdata_file, data=testdata_string)
class TestSyncGcsHook:
    def setup_method(self):
        with mock.patch(
            GCS_STRING.format("GoogleBaseHook.__init__"), new=mock_base_gcp_hook_default_project_id
        ):
            self.gcs_hook = gcs.GCSHook(gcp_conn_id="test")
    @mock.patch(GCS_STRING.format("GCSHook.copy"))
    @mock.patch(GCS_STRING.format("GCSHook.rewrite"))
    @mock.patch(GCS_STRING.format("GCSHook.delete"))
    @mock.patch(GCS_STRING.format("GCSHook.get_conn"))
    def test_should_do_nothing_when_buckets_is_empty(