Emissions workflow enhancements

[rawadelkontar]

Resolves #[issue number here]

Pull Request Description

Restrict emission inputs definition to only site_properties

Checklist (Delete lines that don't apply)

• Unit tests have been added or updated
• Documentation has been modified appropriately
• All ci tests pass (green)
• An issue has been created (which will be used for the changelog)
• This branch is up-to-date with develop

[kflemin]

this looks good! can you add a test that validates a file with emissions data defined, and one that fails when an emissions value (ex: emissions_future_subregion) is wrong? thanks!