Excel Instead Of CSV Export

[naasanov]

Motivation

Currently our parties export to a csv, which does not come with any formatting by default. This would require our users to manually modify the spreadsheet into a readable format. Instead, we should export the parties as a filetype that comes automatically formatted. This should be doable with excel, but anything that comes automatically formatted will do.

Deliverables

• Alter the GET /parties/csv to export a formatted filetype instead of csv
• Update any relevant backend tests
• Ensure the frontend Party Export component still works and produces a formatted file