Viz depends on deprecated "version" top-element being present

[ericslandry]

I was trying to figure out why my viz was no longer working since my refactor towards Docker Compose v2. I started to revert some changes and found that adding a dummy version top-element fixed my viz problem.

The "version" element is no longer mandatory https://github.com/compose-spec/compose-spec/blob/master/spec.md#version-top-level-element and should not be essential to creating a viz.

[jubianchi]

Thanks @ericslandry for reporting this.

The rewrite-v2 branch is introducing many changes among which the fix for the version element.