Comment 6 for bug 1978422

Thanks Mike for the context here and spending time understanding the symptoms.

In our deprecation of this key, we should have also added a DEPRECATED description to this in our schema. Looks like we covered that approach in other keys like `grub-dpkg` -> grub_dpkg[1] and `remove-defaults` -> remove_defaults[2] but not in this case. We have PRs in flight to fix this and will make sure subiquity is also onboard with our deprecation schedule for these keys too so we don't re-introduce this problem when the hyphenated keys are officially dropped in upstream.

References:
[1] https://github.com/canonical/cloud-init/blob/main/cloudinit/config/schemas/schema-cloud-config-v1.json#L760
[2] https://github.com/canonical/cloud-init/blob/main/cloudinit/config/schemas/schema-cloud-config-v1.json#L167