Confusion about the `CommodityType` parameter

The [documentation for this parameter](https://muse-os.readthedocs.io/en/latest/inputs/commodities.html) states that "Service" should be used for end-use commodities such as heating, however the example models/tutorials use "Energy" for the `heat` and `cook` commodities. This is confusing and needs to be clarified.

Looking at the code, "Energy" and "Environmental" are the only `CommodityType` options that are directly referenced. For end-use commodities, the important thing is that they get picked up by the `is_enduse` function, but this will be true for any products that are not the "Environmental" type (so it doesn't actually matter if it's "Service" or "Energy")

Start with the linked CommodityType documentation, then compare the heat and cook examples in the example models/tutorials. Read the is_enduse function and its handling of Energy, Environmental, and Service. Done means the documentation and examples clearly agree on the valid end-use value and explain why.

Written by the indexing model from the issue text.