backoff library for backoff code

[roman-khimov]

Is your feature request related to a problem? Please describe.

I'm always frustrated when we're not using small well-known libraries to simplify our own code.

Describe the solution you'd like

Block uploader has a backoff mechanism of its own, but likely it can be replaced with https://pkg.go.dev/github.com/cenkalti/backoff.

Describe alternatives you've considered

Keep it as is, works fine. But an easy to use backoff library can be reused in more places in future.

Additional context

#3582