feat: recommend Snapcraft 9.x for core22, core24, and core26 bases
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Issue body
## Description
Add a warning message recommending Snapcraft 9.x when building
snaps with core22, core24, or core26 bases.
Closes #4958
- [x] I've followed the [contribution guidelines](https://github.com/canonical/snapcraft/blob/main/CONTRIBUTING.md).
- [x] I've signed the [CLA](http://www.ubuntu.com/legal/contributors/).
- [x] 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.
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