Custom docker images for PHP builds

[Anilm3]

Description

The CI builds for the appsec extension currently use prebuilt binaries provided by a third party. These binaries change without our knowledge or control and occasionally break the builds, so we should build our own docker images with the binaries we require in order to ensure the reliability of our CI and release process.

This could also be expanded to the release builds to avoid using a cache.

The generation of containers could be done in a separate repository, perhaps dd-appsec-php-containers, with actions to be manually triggered with workflow_dispatch (more info here) to allow us to generate only the necessary images.