Use multi-arch building to have arm64 and amd64 images on docker hub

[baschny]

In order to build a multi arch image (arm64 and amd64) on release on docker hub:

• use the buildx action to load the multi-arch capable builder for docker
• use the build-push-action to build and push the multi-arch images (its not possible to do "build" and "push" in separate steps anymore, since the multi-arch build with buildx only supports --push and not --load).

Tested on my own account: https://hub.docker.com/r/baschny/php-extension-installer/tags

Resolves #1005

[mlocati]

Why just linux/amd64 and linux/arm64?

I'd use all the platforms defined by the official PHP images...

For example, for the latest php:8.3 image I see these architectures at https://hub.docker.com/_/php/tags:

• linux/386
• linux/amd64
• linux/arm/v5
• linux/arm/v7
• linux/arm64/v8
• linux/mips64le
• linux/ppc64le
• linux/s390x

(It seems a bit strange to me that an image cannot be defined as "platform independent", but I guess we have to accept it)

[baschny]

Good idea - its so small anyway :) It works: https://hub.docker.com/r/baschny/php-extension-installer/tags, see a750748

[mlocati]

Thanks!

[mlocati]

PS: this required a minor fix - see 2654a69

[mlocati]

And there was a major issue: see #1016 (fixed by 2e59715)