clj-http 3x support

hey, i've made a fork https://github.com/zarkone/aws-sig4 which 

- targets clj-http v3.x ver but drops v2.x support
- uses tools.deps
- uses github actions to publish to clojars: https://clojars.org/org.zarkone/aws-sig4

feel free to ping me if you think it does make sense for you to merge it together