Backup to s3 corrupted whih larger SSTables files

[aharonh]

The known nuvo/skbn issue nuvo/skbn#30 causes scilent failures when larger db files are backed-up to s3. This is due to use of default parameters for s3 multipart upload. To allow larger files upload, enable configuration of s3 max upload parts and s3 part size parameters. Adjust defaults to allow for up to 1.2 Tb files. For larger max files size, make sure to adjust those paramters.

Adding verbose logging information to help detect issues in transfer.