command/cp: add progress bar

[ahmethakanbesel]

Resolves #51

Enables usage of cp command with show-progress flag to show progress bar for a copy task.

Example progress bar: 78.00% ━━━━━━━━━━━━━━━━━━━━──────── 780 MB / 1.00 GB (189.37 MB/s) 5.9s (28/29)

[szeitlin]

love this!

[seruman]

Not related to this PR; https://github.com/peak/s5cmd/actions/runs/5609611887/jobs/10263554721?pr=590

https://github.com/peak/s5cmd/pull/582 introduced flakiness on Windows on cp tests.

[igungor]

The more I use it , the more progressbar's position indicator looks invisible to me :) This is a subjective matter of course, but I'd like to propose a minor change. What do you guys think?

Before:

After: