Provide JSON artifact with details for consumption by archweb
When releasing a new version of the releng build artifacts we require a JSON consumable, that can be picked up by the promotion tooling and/or archweb to add metadata about a new release.
The consumable needs to implement at least the following [attributes from the respective archweb models](https://github.com/archlinux/archweb/blob/c6d91ecbd49b7e593415f51a751e149e3a79ca7d/releng/models.py#L16-L28) for this to work.
Interesting metadata is:
- kernel version
- archiso version
- ipxe version
issue