pkg/errors is obsoleted

[claviola]

The package has been archived on github and doesn't have a maintainer: pkg/errors#245

As seen in the issues linked to it, different projects took different approaches, from replacing usage with a fork to using only standard library modules (fmt and errors itself).

I'm willing to submit a PR for this.

[mitar]

Shameless plug: you can switch it to drop-in replacement gitlab.com/tozd/go/errors. It fixes many issues, is maintained, and supports modern Go's error patterns (sentinel errors, %w formatting, joined errors, etc.).