Relaxing "Too many parts" threshold in ClickHouse for larger partitions

Relax the "Too many parts" threshold. This closes #6551. Now ClickHouse will allow more parts in a partition if the average part size is large enough (at least 10 GiB). This allows to have up to petabytes of data in a single partition of a single table on a single server, which is possible using disk shelves or object storage. #42002 (Alexey Milovidov).