Add support for reading endYear from the public export

[jfly]

We want to add an endYear column to the public export, but we can't because it would break the workbook assistant. See thewca/worldcubeassociation.org#2593 (comment) for more information.

I personally think it would be best for the WA to be re-written so it doesn't depend on the ordering of the columns in the database export.

[AlbertoPdRF]

I personally think it would be best for the WA to be re-written so it doesn't depend on the ordering of the columns in the database export.

I don't know how much work that is, but if it requires a significant amount of work, it may be better to just work towards thewca/worldcubeassociation.org#225 instead.