feat: *_classification files gain publication date

[jacobvjk]

sector classification systems are usually updated at irregular intervals, where a new update is not necessarily compatible with the previous iteration. Sometimes codes are removed, sectors are split along different lines, and new codes are added. We have been made aware of this issue in dealing with Canadian NAICS sector classifications.

Similarly, revisions to sector classifications occur in NACE: https://ec.europa.eu/eurostat/web/nace/overview
And in ISIC: https://en.wikipedia.org/wiki/International_Standard_Industrial_Classification

Our sector classification data sets should therefore gain a column that shows the version of the data that we are referring to.

[jdhoffa]

Seems reasonable and simple enough to add.
Technically happy to do this, I would however need support from you, or an analyst, in terms of defining what dates should be added and where.

[jacobvjk]

I think we probably have to dedicate some time to figure this out and decide which versions we want to support. I don't think we currently really know which ones we are using. I added this feature and would suggest to tackle this issue as part of that: https://dev.azure.com/RMI-PACTA/2DegreesInvesting/_workitems/edit/9852

[jdhoffa]

Makes sense!

FYI. I have added the "help wanted" label, which I am using here to mean "the maintainer of this repo doesn't have sufficient context to tackle this issue independently"

:-)

[jdhoffa]

Is this necessary if the datasets also gain the revision or version column?

[jdhoffa]

Closing in favour of #344