[CBM] [Dev-Tools] cbm_timeline.py should parse and print timings about backup/restore sub-tasks

What's the issue?
'cbm_timeline.py' currently only prints the start/end times for each sub-command in the logs; it would be nice if we could add some additional "nesting" e.g. how long has has it taken to backup/restore each bucket, may even how long did it take to complete multipart uploads/upload Rift indexes (both of these timings are already included in the logs).

I have no idea if this will be possible without, however, it's worth investigating.