Test assetless BAR build creation

[premun]

Context

When we switch to the flat flow, the product repositories won't have their official builds anymore. However, we need to still publish an empty BAR build from their internal pipelines so that subscriptions are triggered. We need to test if publishing an empty build works.

Goal

• Test if it's possible to create an assetless build or if we need to add a dummy package (maybe we somewhere read the version by getting a first package of the build or something).
• If it does not work, we will need to create a YAML template in Arcade which repos could include to publish a build (please create an issue for that).