Extend Data Bucket Stream with Indexing by Ingestion Order
Before, buckets could be only referenced by key which could for example represent a file name. Often it is necessary to access buckets by order of insertion (=order of ingestion of buckets), for example when data is processed in intervals for a monitoring system. This mr adds api methods to reference a bucket either by key or by index. Deprecation warnings have been added for the old api. Test suite is here: https://nexedi.erp5.net/test_suite_module/620/TestSuite_view