After a bunch of recent changes/rebasing our vendored dependencies got a
little out of sync w.r.t transitive dependencies through codebases that
are not themselves Go Modules yet.
Here we upgrade the AWS Go SDK to 1.12.27 and AWS provider to include terraform-providers/terraform-provider-aws#1608.
This includes the capability to use named credentials profiles from the `~/.aws/credentials` file to authenticate to the backend.