Switch from GitHub Actions to AWS CodeBuild

[tfausak]

Exactly what it says on the tin.

Plus this also switches from GitHub's container registry to a public AWS ECR registry: https://gallery.ecr.aws/v6m6o3k4/haskell

And this doesn't tag "latest" builds. You have to select a commit hash in order to use one of the images.

Here's proof that it works:

$ docker run --interactive --rm --tty public.ecr.aws/v6m6o3k4/haskell:9.4.2-ecf08584ca4e459b567721c3a98b5515400d4443 ghci
GHCi, version 9.4.2: https://www.haskell.org/ghc/  :? for help
ghci> putStrLn $ unwords ["Hello,", "world!"]
Hello, world!

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• I manually tested the code locally to make sure that it works.
• If there is documentation, I made sure it's accurate and up to date.
• If possible, I wrote automated tests for the new behavior.