tests: fix test_storage_s3_queue/test_0.py::test_streaming_to_many_views flakiness

The problem is that streaming is done in background and it can be
started when there are less MVs created yet, but in the mean time the
test will create missing MVs and create files in S3.

Here is an example of server logs for such failure [1]:

    2025.04.17 16:08:20.523134 [ 493 ] {} <Debug> StorageS3Queue (default.streaming_to_many_views_ordered): Started streaming to 9 attached views
    2025.04.17 16:08:20.523665 [ 13 ] {4e2228b2-48d9-42c8-bafb-9965d9c74625} <Debug> executeQuery: (from 172.16.1.1:58662) (query 2, line 5) CREATE MATERIALIZED VIEW streaming_to_many_views_ordered_10_mv TO streaming_to_many_views_ordered_10_dst AS SELECT *, _path FROM streaming_to_many_views_ordered; (stage: Complete)
    ...
    2025.04.17 16:08:20.572373 [ 744 ] {} <Test> StorageObjectStorageQueue(/clickhouse/test_streaming_to_many_views_ordered_ddxwkh): Path: streaming_to_many_views_ordered_data/a_0.csv, node_name: 5331496251994711888, max_loading_retries: 2, processed_path: /clickhouse/test_streaming_to_many_views_ordered_ddxwkh/buckets/0/processed, processing_path: /clickhouse/test_streaming_to_many_views_ordered_ddxwkh/processing/5331496251994711888, failed_path: /clickhouse/test_streaming_to_many_views_ordered_ddxwkh/failed/5331496251994711888

  [1]: https://s3.amazonaws.com/clickhouse-test-reports/json.html?REF=master&sha=79015e3ac01920269c1789b176fcc739ae9bbaca&name_0=MasterCI&name_1=Integration%20tests%20%28tsan%2C%201%2F6%29

Sadly, but there is no way to sync this things without extra sleep.

Author: azat

tests/integration/test_storage_s3_queue/test_0.py

@@ -441,6 +441,9 @@ def test_streaming_to_many_views(started_cluster, mode):
     expect_rows_num = [0]
     files = []
 
+    # ensure that streaming from S3 will be started only once all MVs has been created
+    time.sleep(5)
+
     def generate_files(files_num=20, row_num=100, file_prefix = "a"):
         files.extend(
             [