Build for arm64 as well as amd64

[jellybob]

I'm not sure whether this actually works or not, but theoretically it should result in making arm64 images available for people running on recent Apple machines rather than having to translate from amd64 which sucks up battery life at an impressive rate.

Annoyingly this isn't a complete solution as PostGIS doesn't have ARM builds on Docker Hub, but it does get us most of the way there I believe.

[marksteward]

I'm guessing this doubles the build time. Can we use a build matrix to target simultaneously?

[jellybob]

This might be doing a matrix build, assuming I've properly read the Github Actions docs. I've got no idea how to actually test it since builds only happen for main.

[marksteward]

Looks right to me!

[jayaddison]

I've got no idea how to actually test it since builds only happen for main.

One important-ish note for testing: it's probably best to change the image tags from latest to testing-1066 or something so that they don't risk being deployed unintentionally.

Because this branch/PR are opened from within Website repo, I think you could modify the trigger conditions to on: push, branch: build-arm64-images or similar, and that should initiate a workflow run from this branch (just make sure to remember to revert that when satisfied with the testing results).

(I say this as someone who generally tests GHA changes by hackily making changes from a repository main branch :/ )

[jayaddison]

it's probably best to change the image tags from latest to testing-1066 or something so that they don't risk being deployed unintentionally

This was a result of a misunderstanding on my behalf, I think: the deployment workflow uploads the container image(s) to Docker Hub, so the presence of an ARM64 image in addition to existing images shouldn't cause any problems, I suppose? (if so: no need for the image tag rename, after all)

@jellybob had you seen / are you following along with postgis/docker-postgis#256?

[jellybob]

Closing until Github Actions has ARM runners, at which point I'll take another pass at this.