scaleway/compute-instance v5.7.0

compute-instance gains a new optional instance_config.enable_heic_transcoding field (default false, unchanged behavior). When set to true, the instance installs an ffmpeg build with libheif-based HEIC decode support via ppa:savoury1/ffmpeg4.

This exists for pigeon-cli transform --input-file-type=heic: Ubuntu's default apt ffmpeg build (this module's ubuntu_jammy default image) typically does not include libheif support, so transform would otherwise fail fast on the first .heic file with ffmpeg's own "decoder not found" error.

See ADR-0150 for the full design, including why this is net-new provisioning (neither this module's existing packages: list nor its pigeon-cli bootstrap script touch ffmpeg today) and why a PPA was chosen over a static build (consistency with the module's existing Cockpit/Alloy apt-repo pattern).

#257