s3_upload_* session settings

These settings are available in system.settings and are autogenerated from source.

s3_upload_part_size_multiply_factor

Multiply s3_min_upload_part_size by this factor each time s3_multiply_parts_count_threshold parts were uploaded from a single write to S3.

Each time this number of parts was uploaded to S3, s3_min_upload_part_size is multiplied by s3_upload_part_size_multiply_factor.