Add support for descriptive/passthrough data within the YAML schema

[jmorrisnrel]

What can be improved?

Calliope currently takes almost any value in the YAML and adds it to the underlying model along one or more of the indices. It would be nice to have an option to add relevant technology data that doesn't affect the Calliope optimization (a description or parameters needed for post-processing or a downstream model) in the YAML without it being added to the underlying problem. Something like an extras key in a tech/node block that is ignored by the schema and attribute dict code would allow users to put additional context directly into the configuration. The alternative of having the extra data in a readme or other metadata file would work, but having that context directly next to the model configuration would make it easier to review models and diagnose issues.

Version

v0.7.0.dev4

[brynpickering]

I think this will be solved by the solution to #642. If math-related parameters are explicitly defined, then all other inputs are effectively "extras" and won't make their way into the backend in any form.