Add config.prod.example.yaml file

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Currently, config.prod.yml is being tracked by Git, which poses a serious security risk as it may lead to accidental exposure of sensitive production credentials. If credentials get committed and pushed, they could be permanently exposed in the repository's history, making them vulnerable to misuse.

To enforce better security practices and ensure smooth onboarding for contributors, we should:

1. Add a config.prod.example.yml file with placeholder values.
2. Stop tracking config.prod.yml and add it to .gitignore.