Use https://github.com/docker/github-builder to build and push image

[yubiuser]

What does this PR aim to accomplish?:

Use https://github.com/docker/github-builder to build and push image.
It's the same we use now in https://github.com/pi-hole/docker-pi-hole/blob/development/.github/workflows/build-and-publish.yml.
It reduced complexity a lot and offloads maintenance to the resueable workflow maintainers.

Supersedes #149

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[PromoFaux]

Thanks for looking at this - it was on my todo list to get around to!

[yubiuser]

If you feel like porting some ideas from #135 feel free to push to this branch.
I already submitted docker/github-builder#158 which can be useful for our slow and fragile RISCV friend here

[yubiuser]

Look how nicely it re-used the cache (RISCV finished in 47 secs) 🥰

[rdwebdesign]

Are there any disadvantages/downsides to not signing the images?

[yubiuser]

We don't get

Signed SLSA provenance for every build.
BuildKit generates SLSA-compliant provenance attestation artifacts that are signed with an identity bound to the GitHub workflow. Downstream consumers can verify:

which builder commit produced the image
which source code commit produced the image
which workflow and job executed the build
what inputs and build parameters were used

We reduce down stream supply chain security a bit if we don't sign.

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P.s. so far we also did not sign the image.