Add multierror

[rumpl]

docker/api/multierror wraps go-multierror from hashicorp with our default error formatting.

Sample output:

❯ ./bin/docker --context moby context rm test one two
Error: context "test": not found
Error: context "one": not found
Error: context "two": not found

❯ ./bin/docker --context moby rm test one two        
Error: container "test": not found
Error: container "one": not found
Error: container "two": not found

[rumpl]

Build is passing

[rumpl]

There's a lot of wrapping here but it's needed... There is a PR opened that could help this but it's still not merged and it's from 2016, I commented on it, we'll see if hashicorp is willing in merging a PR that would make it possible to define a global formatting function.

[chris-crone]

LGTM

I really like this approach for the CLI errors. We should get @justincormack to review this for UX.