Meta ticket: donate rewrite backend MVP

Splitting off from #111 (closed)

MVP for backend

• Handle stripe donations
  • pick new stripe checkout flow. our current stripe checkout system is deprecated, we'll need to decide on the correct flow to use for the new site
  • implement the new flow in the backend (single and recurring donations), expose a very basic frontend for testing stripe checkout
• Handle paypal donations on the backend
  • audit current paypal checkout flow, ensure that we don't have issues like our stripe checkout
  • implement paypal checkout, single and recurring donations
• List wallet addresses - django setup, yes (donate-neo!1 (merged))
• A link to BTCPay (non-integrated) - django setup, yes (donate-neo!3 (merged))
• Noscript error - django setup, yes (donate-neo!4 (merged))
• CRM integration (that meets Fundraising's specs)
  • Newsletter signup
  • report donations to civi
  • query current perks from civi
• Donation amount array
• Swag display & logic (+ ability to decline swag)
• CAPTCHA
• Simple YEC Ticker (donate-neo!6 (merged))
• Simple order summary (donate-neo!7 (merged))
• Redirect to existing thank you page? maybe? or a simple version for the MVP

Post-MVP

• Ability to track donations made directly through paypal (not through donate.tpo) and report them to civi (tpo/anti-censorship/pluggable-transports/snowflake-webext#79). this can be implemented in the backend with paypal webhooks.
• CMSable/lektorable content [e.g., ability to make new/standalone pages] (possibly with wagtail?)