Spreadsheet Request: Add filter 'to' and 'from' dates

[esurface]

Allow data analyst to specify a "date filter" for downloading spreadsheets. They can currently specify a 'year' and 'month'. Their should be two entries, to specify the "From" year-month and the "To" year-month.

From: "Jan 2023" To: "Nov 2023"

After discussion, this requires neither changes to the couchdb view nor the csv generation API.