Add broadcast_param_data config option and default it to False.

[brynpickering]

Fixes #615

Summary of changes in this pull request

• config.init.broadcast_param_data boolean option available as per suggestion from @irm-codebase. It defaults to False, so must be set knowingly by the user to True to allow for indexed parameter data broadcasting.
• Updated example models to use CSV cost data (national scale) and to have a top-level interest rate (since we don't change it per technology in our example models).
• Updated docs to include this info and reflect updates to example models.

Reviewer checklist

• Test(s) added to cover contribution
• Documentation updated
• Changelog updated
• Coverage maintained or improved

[FLomb]

Thanks for this PR @brynpickering; it looks like a very good solution to issue #615, while it simultaneously enriches the documentation by providing an example of cost data loading from tabular files.

I couldn't check that the docs build properly (see specific comment), but the rest looks ready to approve. Before giving the green light, I would like to perform only a test with some of the models that led me to find the issue in the first place so that I can confirm this solution works in practice. I will do so later today.

[FLomb]

If I look at the 'built' markdown file here on GitHub, the links to files and to the header do not work properly, but I assume this is because these files are built into documentation by Calliope in a different way than simple markdown visualisation. So perhaps someone else who knows how to build the docs locally can double-check that all is as expected

[brynpickering]

@FLomb thanks for checking. You can see the rendered documentation by clicking on the RTD build "details" in the checks:

[FLomb]

Ok, I have tested this on a practical case, and it works as expected; it also nicely warns me if I have a dimension mismatch when switching the broadcast to False.

[irm-codebase]

Gave a glance at how the code is arranged for this change. Looks fine to me!

In the future we might want to turn this type of broadcasting individually per parameter, but let's keep things simple for now.

[brynpickering]

Yep, agreed that per-param broadcasting config is a nice-to-have @irm-codebase - it can be added to the longer-term roadmap.