Add yamllint CI and add yamlfmt pre-commit hook

[grische]

This commit adds a CI for yamllint and adds a pre-commit hook for yamlfmt.

These two together will avoid issues like these https://github.com/NVIDIA/GenerativeAIExamples/pull/225

The PR also has a third commit to fix some issues on the current yaml files (like duplicate keys, invalid formatting, etc) and also applies ymlfmt on the remaining files.