[SSF-183] add FM dashboard endpoint

[amywng]

ℹ️ Issue

Closes SSF-183

📝 Description

• added controller and service method for getting the next two upcoming donation reminders
  • controller endpoint: /manufacturers/:foodManufacturerId/next-two-donations
  • service method: getUpcomingDonationReminders
• wrote controller/service tests

✔️ Verification

tested endpoint on postman and verified tests pass

🏕️ (Optional) Future Work / Notes

not sure if it's just me but /manufacturers/:foodManufacturerId/donations is causing an error/not working...

[sam-schu]

sorry for the delay!

The service function logic does not fully handle the third bullet in the ticket (the case where both upcoming reminders could be for the same donation). For example, testing with a once-weekly recurrence starting 4/15 and a once-monthly recurrence starting 5/11 returned those two dates, rather than 4/15 and 4/22. (It's only weekly donations that recur on multiple days of the week that will have multiple dates in their next_donation_dates array, so we need to handle more than just that case)

[sam-schu]

It looks like the logic updates only change how weekly donations are handled, but we need to handle all recurrence types - e.g., a monthly donation could recur twice before a yearly donation, or a yearly donation could recur twice before an every-3-years donation