The latest version of the go sdk has deprecate the s3 manager in
favor of the new transfermanager. This updates to the new
transfermanager functionality for the two places we were using
the manager, iam s3 and integration tests.
This also removes the pinning of nats nkeys since they have fixed
the tags in their repo now. And general cleanup of the go.mod.
The go mod cache is listing a newer version than the latest tag in
the repo. So we need to pin this older version to prevent dependabot
from updating until the repo tags a newer version.
Ben McClelland