Publishing infrastructure

[michaelmcandrew]

We want to automatically publish this each time a new version of CiviCRM is released, and each time a new version of PHP is released.

We also want to be able to trigger a build on an adhoc basis, for example if there is a security release of a package that we depend on, e.g. something that we are apt installing like libpng-dev.

We've created a script to do this: build.php.

We now need

• a build environment that can build multi platform images (see https://docs.docker.com/reference/cli/docker/buildx/ for more info).
• a way of triggering the build automatically