Verify YAML structure with automated check

[carlopi]

See title.

There have been PRs where YAML structure is different than intended (say string vs list or similar), but failure mode it's not super helpful or clear.

It would be nice, both for contributors AND for (automated) reviewers to have a YAML validator in place

[adriens]

I will probably tr something 🤔 around cue

• 🛡️ First try to CUE validation for description.yml files #1170