Serialisation aliases

[penelopeysm]

Companion PR to https://github.com/Urban-Analytics-Technology-Platform/popgetter/pull/130.

Merge that first and regenerate all the BE/NI data before testing this PR! The CI is failing now because the proposed changes do not match our current data.

This PR:

• Reworks the function which joins all metadata tables to use the new column names.
• Defines all the column names in a single struct impl, and gets rid of all the remaining magic constants.

It would be cool if we had a test to get the column names from upstream Python and check that they are equal to the ones here. I haven't done that, though. Alternatively, if we one day merge the two repos into one, they could potentially be derived from the same file.

[penelopeysm]

The tests don't currently pass. However, they should (hopefully!) pass if you do either one of these:

• Regenerate all the upstream data (now that the previous PRs have been merged) and place it in the popgetter-dagster-test Azure container
• Point the config base path instead to https://popgetter.blob.core.windows.net/prod/0.1.0, where I've uploaded a subset of the Belgium and NI data (enough to make the tests pass, anyway).

[sgreenbury]

Thanks for this @penelopeysm, looks great!

I've just updated the config b131f59 to point to a path with the new data (will open an issue to point to modify to point to same path as the final released data) and added a few small comments/queries above in the code.

[sgreenbury]

Merging this now, thanks @penelopeysm!