Use something other than github.com/pkg/errors

[matthchr]

Describe the current behavior

We're using github.com/pkg/errors

Describe the improvement

use something else - above is deprecated/archived.

Additional context

Add any other context about the suggested improvement.

[theunrepentantgeek]

After a discussion with @babbageclunk, I think we'll switch to github.com/rotisserie/eris - it has a near identical API, so the switch should be straightforward.

[theunrepentantgeek]

I think migration might be fairly simple, as we can use gopatch to make many of the changes.

Provisional plan:

• Code Generator (v2/tools/generator) Migrate code generator to eris #4454
• Generated code (v2/api) Migrate generated code to eris #4453
• Controller (v2/pkg and v2/internal)
• asoctl (v2/cmd/asoctl)
• Test reporting (v2/tools/manglejson)

At this point we'll likely have a few remnants requiring manual work to eliminate.