fix(ci) :: refactor image build step to include amd64

[81reap]

docker_build_amd64_minimal was a copy of docker_build but for amd64 as it does a few extra things (1) doesn't need QEMU, (2) builds a tarball for Hurl testing, and (3) some extra cache scope.

Now it joins the docker_build matrix with the flag export: true to gate the extra steps needed for amd64. This cleans up the CI and makes upgrading other platforms to also export a feature flag change rather than a CI refactor.

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[lovasoa]

Run actions/download-artifact@v8
Downloading single artifact
Error: Unable to download artifact(s): Artifact not found for name: sqlpage-linux-amd64-minimal-image
        Please ensure that your artifact is not expired and the artifact was uploaded using a compatible version of toolkit/upload-artifact.
        For more information, visit the GitHub Artifacts FAQ: https://github.com/actions/toolkit/blob/main/packages/artifact/docs/faq.md

Looks like the ci changes don't build the image the tests need anymore ?

[81reap]

actually I think that's just a transient failure in the CI. rebasing on mainline seems to have fixed it

edit :: missed including the CI link https://github.com/sqlpage/SQLPage/actions/runs/36005310697

[lovasoa]

@81reap I think this wasn't a transient failure and it broke ci on main.

[lovasoa]

You removed the dependency of the hurl tests on the job that creates the docker image they use !