Switch to aws-sdk-go-v2 vendored library

[dims]

trafficstars

aws-sdk will be going away next year-ish... please see announcement here: https://aws.amazon.com/blogs/developer/announcing-end-of-support-for-aws-sdk-for-go-v1-on-july-31-2025/

Let's please start switching to the new aws-sdk-go-v2

Looks like several projects in k8s github orgs have already done so! https://cs.k8s.io/?q=aws-sdk-go-v2&i=nope&files=go.mod&excludeFiles=&repos=

cc @cartermckinnon @kmala @prateekgogia