Support syncing from remote CSV (Google Sheets)

[patcon]

Builds on #3 :)

If building from CSV is doable, then we can add code to download the CSV from a public Google Sheet, and cofigure the starter pack / feed from that :)

This would simply involve downloading a CSV from a URL when provided, instead of looking locally in the repo.

Pros:

• allow anyone who knows how to use Google Sheets to edit the starter pack
• access control via google collaboration tools (very established)

Cons:

• can't auto-detect changes, so would need to run CI on schedule, but not immediately updated (there are interesting mitigations by poking the the "workflow dispatch" endpoint in the GitHub API, but more on that in another PR ;) )

[jaseemabid]

I actually started writing this code yesterday with a Google sheets backend in mind, but their auth is complicated enough that I gave up and picked a dead simple text file instead. This would be a good addition unless the code and auth setup gets a lot more complicated.

[patcon]

Yay! public/published sheets (there might be a difference) just allow fetching a CSV from the export url fwiw. So shouldn't need complicated google auth.

Happy to scope later