cleanup: don't use pkg/errors

[imjasonh]

- What I did

Replaced uses of github.com/pkg/errors in this repo.

That package has been archived for 2 years, after fmt.Errorf added support for wrapping errors with %w in Go 1.13, more than 3 years ago.

There are still indirect dependencies on pkg/errors via github.com/docker/docker -- I can try to clean those up as well, if you're interested.

- How I did it

Mostly I ran this: https://github.com/zchee/go-analyzer/tree/main/pkgerrors

pkgerrors -fix ./...

In order to get that to work though, I first needed to find cases where errors.Wrap was called like errors.Wrap(err, msg) (where msg is an identifier and not a const string expression) or errors.Wrap(err, foo()) (where foo is a method call and not a const string expression).

After that I replaced any remaining errors.Is calls to use Go's stdlib errors.Is, which now works with the %w added by the analyzer

- How to verify it

Thorough code review and reliance on tests

- Description for the changelog

Remove use of deprecated/archived module github.com/pkg/errors

TODO (if you're interested in proceeding)

• fix lint findings now that fmt.Errorf with capitalized message trips the linter
• do github.com/docker/docker too