Fix and automatically scales to high request

S3 partitions objects internally based on key-name prefixes and automatically scales to high request rates per partition. This change introduces two new BACKUP settings: data_file_name_generator and data_file_name_prefix_length. When data_file_name_generator=checksum, backup data files are named using a hash of their contents. Example: for a checksum = abcd1234ef567890abcd1234ef567890 and data_file_name_prefix_length = 3, the resulting path will be: abc/d1234ef567890abcd1234ef567890. The resulting key distribution enhances load balancing across S3 partitions and reduces the risk of throttling. #88418 (Julia Kartseva).