2026.1: Package repos for kolla image builds

[Alex-Welsh]

Creating this PR for discussion only right now.

The way kolla configures package repos has changed a lot in the latest release and I need to work out the best way to do it. That might require some changes to kayobe or kolla iself to expose the right variables and make this easier than it has been in previous releases.

[gemini-code-assist]

Code Review

This pull request removes support for Rocky 9 and introduces repository configurations and definitions for Rocky 10 and Ubuntu Noble across several files, including kolla-build.conf, repos.yaml, and stackhpc.yml. Feedback on these changes includes updating an outdated comment in kolla-build.conf that still references Rocky 9, removing repository definitions for CentOS Stream 10 and EL10 since they are not yet officially supported, and converting a multi-line gpgkey string in repos.yaml to a single-line format to avoid potential parsing errors.

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[Alex-Welsh]

Alright, I think this is ready for review now. It's obviously not functional yet, but I'd rather do this piece-by-piece than do unmergable mega-commits.