Add a SystemUsernames pydantic model with snap_daemon marked as deprecated, so the JSON schema exposes 'deprecated: true' on that key. Also emit a runtime warning via craft-cli when snap_daemon is used. Fixes: https://github.com/canonical/snapcraft/issues/5448 Describe your changes. --- - [ ] I've followed the [contribution guidelines](https://github.com/canonical/snapcraft/blob/main/CONTRIBUTING.md). - [ ] I've signed the [CLA](http://www.ubuntu.com/legal/contributors/). - [ ] I've successfully run `make lint && make test`. - [ ] I've added or updated any relevant documentation. - [ ] In documents I changed, I [added a meta description](https://canonical-starflow.readthedocs-hosted.com/how-to/add-a-page-meta-description/) if one was missing. - [ ] I've updated the relevant release notes.